Bio- unit 1-pt3- book notes- ch 13, 14, 15

Because not all organisms are preserved, the fossil record is not a complete ---of past life. Nevertheless, the existing fossil record is remarkably rich and offers a revealing window into the past.

record

EVOLUTION FITNESS NATURAL SELECTION

Change in allele frequencies in a population over time. The relative ability of an organism to survive and reproduce in a particular environment. Differential survival and reproduction of individuals in response to environmental pressure that leads to change in allele frequencies in a population over time.

What can anatomy and DNA reveal about evolution?

When combined with evidence from the fossil record, anatomy, development (and biogeography, a fourth line of evidence, discussed in Chapter 16), molecular data become a powerful tool for understanding evolution. As we'll see in Chapter 16, DNA evidence is often a more reliable clue to common ancestry than is physical appearance, and can serve as a check on conclusions derived from the fossil record or anatomy. "It confirms that we have a very good understanding of the framework of the history of life,"

Natural selection doesn't always affect populations in the same way. By studying how natural selection has shaped populations, scientists have identified three major patterns of natural selection

When the environment favors an extreme phenotype, causing the population to shift in one direction over time, directional selection has occurred. The emergence of antibiotic-resistant bacterial populations is a good example of directional selection. -ex The environment created a selection pressure which favored giraffes with longer necks who could reach more food in the trees. At the same time, there was selection pressure against giraffes with shorter necks. Both long and short necks are extreme phenotypes, but over time, the long neck phenotype dominated due to selection pressure, i.e., this trait in giraffes shifted toward the direction of long necks. When the environment favors the middle of the phenotypic spectrum, and extremes are selected against, we call this stabilizing selection. -ex Infants with low birth weight will be weak and experience health problems, while large babies will have problems passing through the birth canal. Babies with average birth weight are more likely to survive than a baby that is too small or too large. when the environment favors the ends of a phenotypic spectrum, diversifying selection occurs. -ex If the pollinator that prefers medium-height plants is removed, natural selection would select against medium-height plants and the overall plant population would move toward having only tall and short plants, the two extreme phenotypes.

Bacteria are ----: in the air, in food, on toothbrushes and computer keyboards—even on and inside you. Your body hosts a wide variety of bacteria, ranging from helpful ones like Lactobacilli and Bifidobacteria that live in the gut and aid digestion to harmful ones like Salmonella that cause food poisoning. There are more bacteria living on and in you than there are human cells making up your body.

everywhere

How Fossils Are Dated

Relative Dating - dating relative to surrounding rock layers. not directly dated but dated relative to the age of the rock layers that bracket them radiometric dating - rock layers formed from volcanic eruption can be directly dated by measuring the products of decay of radioactive elements presents in those layers. fossils found are the same age as the rock. dating relative to other fossils - relative to other findings. found in deeper sediment layers that are deeper then the earth are generally older than those found in layers closer to the earths surface.

POPULATION GENETICS GENE POOL ALLELE FREQUENCY NONADAPTIVE EVOLUTION

The study of the genetic makeup of populations and how the genetic composition of a population changes. The total collection of alleles in a population. The relative proportion of an allele in a population Any change in allele frequency that does not by itself lead a population to become more adapted to its environment; the mechanisms of nonadaptive evolution are mutation, genetic drift, and gene flow.

Of the body sites highlighted, where is staph most likely to be found?

skin

How do different evolutionary mechanisms influence the composition of a gene pool?

Over time, several forces can change the frequency of alleles—that is, how common they are in the population This can occur by a variety of mechanisms, including mutations, natural selection, and genetic drift. The result is a gene pool that is altered to be attuned to the needs of the population's specific environment. Because it is rare, mutation by itself does not dramatically change allele frequencies. But that doesn't mean it isn't important—after all, mutation is the source of variation in a population, upon which natural selection acts.

How do the daughter cells produced by binary fission compare to each other and to the parent cell?

The daughter cells are genetically identical (unless a mutation occurs during replication). In binary fission, the fully grown parent cell splits into two halves, producing two pools. ... The genetic material is replicated, then equally split.

Monkey Business quiz 1 With respect to human beings, race is best described as: 2 Human and chimpanzee DNA is 99% identical. How similar is your DNA to ANY other human on the planet (regardless of race)? 3 The primary pigment that determines human skin color is ___ and it is produced by ___. 4 Biological factors that are known to correlate with skin color are: 5 Which of the following is not an example of a functional trait of living organisms? 6 Which of the following organelles are found in both plants and animals? 7 Cell theory states that: 8 A distinguishing feature of eukaryotic cells is that they 9 What occurs in natural selection? 10Most bacteria are harmful and cause deadly diseases. 11 Taking antibiotics when you are sick is causes ____ selection within populations of bacteria. 12 When you have a cold, you should take an antibiotic. 13 You wish to test the effects of energy drinks on short-term memory in college students. You recruit 100 volunteers for your study. The control group will receive a placebo and the experimental group the same volume of Red Bull. You will administer a test of short-term memory 30 minutes after participants consume their drinks. Should the control group in this Red Bull Experiment know that it is receiving the placebo? 14 A front-page story in your local paper states that drinking three cups of coffee a day lowers the risk of heart disease. A month later, the same paper carries a new story stating that drinking coffee increases the risk of heart disease. Assuming that both conclusions stem from well-designed studies, how can you explain these contradictory stories?

1 A social construct, based mainly on superficial characteristics like skin colo 2 99.9% 3 Melanin; specific skin cells 4 - Folate levels -Vitamin D production -Protection against UV light 5 Obtain and use energy from the sun 6 Ribosomes and Mitochondria 7 all living things are composed of cells. and cells come from other cells. 8 contain a nucleus and other organelles. 9 change in allele frequency over time. 10 False 11 directional 12 False 13 No, so you can take the placebo effect into account. 14 -The amount of caffeine in the coffee used in the two studies might differ. - The ages of the subjects in the two studies might differ. - One study might have been conducted on women while the other was conducted on men. - One study might have been done on smokers and one on non-smokers

1 The ancestors of modern humans evolved in a high-UV environment. What does this suggest about their skin color? 2 In the course of human evolution, which of the following environmental factors likely influenced whether a population had mostly light-skinned individuals or mostly dark-skinned individuals? 3 Jablonski and Chaplin hypothesized that darker skin is advantageous in __________ UV environments because darker skin ___________. 4 Which of the following would help darker-skinned people who live in low-UV environments remain healthy? 5 What can you infer about the skin-color alleles and the geographic origins of the ancestors of a light-skinned person and of a dark-skinned person?

1 Our modern human ancestors in Africa likely had dark skin, which is produced by an abundance of the pigment eumelanin in skin cells. In the high-UV environment of sub-Saharan (or equatorial) Africa, darker skin offers protection from the damaging effects of UV radiation. 2 Levels of UV light 3 high; protects folate from degradation 4 vitamin D supplements 5 A dark-skinned person would have more alleles to produce melanin.

Java Report quiz 1 What is the DEPENDENT Variable? A scientific study looked at the effect of tanning beds on DNA, specifically DNA damage. The scientist took skin cells and exposed them to UV radiation (the type used in indoor tanning beds) for different lengths of time some for 1 minute, some for 5 minutes, some for 15 minutes, and some for 30 minutes. They then looked for signs of DNA damage and compared the results to cells that had never been exposed to UV light. 2 What is the INDEPENDENT Variable? A scientific study looked at the effect of tanning beds on DNA, specifically DNA damage. The scientist took skin cells and exposed them to UV radiation (the type used in indoor tanning beds) for different lengths of time some for 1 minute, some for 5 minutes, some for 15 minutes, and some for 30 minutes. They then looked for signs of DNA damage and compared the results to cells that had never been exposed to UV light. 3 Different scientific studies have drawn different conclusions about the risks and benefits of coffee. What norm of science is best represented by this example? 4 You are listening to a news report that claims a new study has found convincing evidence that a particular weight-loss product is much more effective than diet and exercise. What can you infer about the "convincing evidence" in this case? 5 Where are the most reliable scientific results published? 6 What is the importance of peer review in the scientific process? 7 Which of the following plays a factor in misrepresentation of research data in the media? 8 A correlation in a scientific study indicates 9 You are reviewing the results of five similar experiments, but each had a different sample size. Which of the following experiments has the most reliable results? 10 What is the importance of statistical analyses?

1 The amount of DNA damage 2 The length of time the cells are exposed 3 All scientists differ in their backgrounds and experience, so different individuals may examine the same evidence and draw different conclusions. 4 Statistical tests showed significantly more weight loss in the participants who used the weight-loss product than those who relied on diet and exercise. 5 in peer-reviewed scientific journals 6 It ensures that a study has been appropriately designed and correctly interpreted. 7 -lack of understanding of the topic by the reporter -overstating the importance of the study results by the researcher -misinterpretation of the scientific terminology when trying to disseminate it to the public time and space limitations by the media 8 a possible link between two variables. 9 the experiment with a sample size of 100,000 10 They can be used to either support or reject the hypothesis, or to determine whether any observed differences between two groups are real or a result of chance

19 Scientists rely on evidence from the fossil record to determine how and when events in human evolution occurred. Which of these major milestones in human evolution is not correctly dated? 20 A person's skin tone is not caused by ___________. 21 Which of the following statements is not a correct relationship about how the UV light environment affects humans? what is it then? 22 Place the evolutionary milestones in order from first to most recent 23 pigment produced by a specific type of skin cell that gives skin its color 24 essential nutrient, necessary for basic bodily processes like DNA replication and cell division 25 What type of cell produces the pigment molecule that gives dark skin its color?

19 The most recent common ancestor of chimpanzees and humans was Ardipithecus ramidus, which lived 4.4 million years ago. 20 Whether or not the person is related to the "mitochondrial eve" or the last common female ancestor 21 In a high-UV-light environment, skin color is more likely to be lighter. - the weaker the UV light, the fairer the skin 22 1. ability to walk upright2. tool use3. use of fire4. big brain 23 melanin 24 folate 25 Melanocytes

6 Our closest primate relatives, chimpanzees, have light-colored skin yet live in tropical (high-UV) environments. How would the Jablonski-Chaplin hypothesis explain this observation? 7 Vitiligo is a disease in which melanocytes are destroyed, with resulting loss of pigmentation. a) If a dark-skinned person develops vitiligo and therefore lighter-colored skin, will his or her race change? b) Given your answer to part a, can you think of one or more factors that might have led people to classify (or misclassify) themselves or others as members of one race or another? 8 Who is mtEve, and when did she live?

6 The hair of chimpanzees protects their light skin from UV light 7 a) no b) ??? 8 All modern-day humans can trace a portion of their genetic ancestry back to a single woman, Mitochondrial Eve, who lived 200,000 to 150,000 years ago in Africa

9 The following three types of DNA can be used to trace evolutionary history. Match each DNA type with the best description of how it is transmitted in a population. _____mtDNA - useful tool in the study of human evolution _____nuclear DNA _____Y-chromosome DNA 10 According to the out-of-Africa hypothesis of human origins and migration, which group of people should show the highest level of genetic diversity?

9 -Mitochondrial DNA is inherited only from the mother and does not undergo recombination. Thus, it is transmitted intact from mothers to all their children and so can be used to trace a lineage. As mitochondrial DNA mutates at a constant rate, it is possible to use it as a molecular clock to estimate the time since different lineage diverged. -It is inherited by all children from both their mothers and their fathers. - inherited only by sons from their father 10 Africans

ANTIBIOTIC . BINARY FISSION POPULATION GENE TRANSFER

A chemical that can slow or stop the growth of bacteria; many antibiotics are produced by living organisms A type of asexual reproduction in which one parental cell divides into two. A group of organisms of the same species living together in the same geographic area. The process by which bacteria can exchange segments of DNA between them.

PALEONTOLOGIST RADIOMETRIC DATING RELATIVE DATING INVERTEBRATE TETRAPOD HOMOLOGY

A scientist who studies ancient life by examining the fossil record. The use of radioactive isotopes as a measure for determining the age of a rock or fossil Determining the age of a fossil from its position relative to layers of rock or fossils of known age. An animal without a backbone. A vertebrate animal with four true limbs, that is, jointed, bony appendages with digits. Mammals, amphibians, birds, and reptiles are tetrapods. Anatomical, genetic, or developmental similarity among organisms due to common ancestry.

Mitochondrial Eve shows that Homo sapiens is a relatively young species, having first evolved in ---between 200,000 and 150,000 years ago. But Eve's family—our family—was just one of many other human families that existed at the time, in Africa and in other places around the world. The term "human" refers to our genus name—Homo. There were many other members of the genus Homo—many other ancient humans—that once roamed the globe. But our single species—Homo sapiens—is the only one that did not eventually die out. Moreover, these other Homos are just our immediate evolutionary relatives. Our extended family tree includes living and extinct primates belonging to the biological family Hominidae (also known as the great apes). These hominids include humans, orangutans, gorillas, chimpanzees, and bonobos.

Africa

s Munshi-South points out, cities are active contributors to the evolutionary process, shaping the wildlife around us in profound ways. Along with climate change, ---is one of the main ways in which humans are directly altering the face of the planet and thereby shaping the fate of species.

urbanism

6 Which of the following statements apply to the founder effect? 7 Which of the following are examples of genetic drift? 8 A bottleneck is best described as 9 A population of ants on a median strip has 12 different alleles, A through L, of a particular gene. A drunk driver plows across the median strip, destroying most of the median strip and 90% of the ants. The surviving ants are all homozygous for allele H. a) What is the impact of this event on the frequency of alleles A through L? b) What type of event is this?

6 It decreases genetic diversity. It is a type of genetic drift. 7 founder effects and bottlenecks. 8 a reduction in the size of an original population followed by an expansion in size as the surviving members reproduce. 9 a)-The frequency of alleles A through L has changed drastically.-All frequencies except H are reduced to zero.-H frequency is now 1.0 b).-This event is an example of a bottleneck effect.

Biologists refer to two general types of genetic drift: founder effects and bottlenecks.

A founder effect occurs when a small group of settlers ("founders") splits off from a main population and establishes a new one. Because a founding population is by definition small, there is a good chance that the particular alleles it carries will not be fully representative of the population it left. Thus, founder effects tend to reduce the genetic diversity of the new population. When a population is cut down sharply—forced through a "bottleneck"—there's a good chance that the remaining population will possess a less-diverse gene pool. Bottlenecks can occur from natural causes—say, a flood that sweeps through the city, killing many individuals—or from human interference, such as the clearing of a forest. Either way, a population that is forced through a genetic bottle neck usually contains a fraction of the original diversity in the population

Evolution by Natural Selection

A typical population of organisms, individuals will vary genetically. When the virus in favor some genetic variation over others, those variance will have a higher fitness and they will survive better and reproduce more successfully. Over generations, the frequency of alleles that confer higher fitness will increase. For those that confer lower fitness will decrease. This non-random challenge in alleles frequencies over generation is called evolution by natural selection In the absence of anabiotic 1- individual bacteria in the population have about the same fitness 2- individuals reproduce at about the same rate and therefore pass on their alleles in similar numbers to the next generation 3- over time, the frequency of alleles remain the same In the presence of antibiotics 1- resistant bacteria have higher fitness, sensitive individuals cannot reproduce at all. 2- resistant bacteria reproduce more often and therefore pass on their resistant alleles in greater numbers the next generation 3- overtime, the frequency of resistant alleles increased dramatically

CHAPTER 14 SUMMARY

From a genetic perspective, a population is identified by the particular collection of alleles in its gene pool. Genetic diversity, as reflected by the number of different alleles in a population's gene pool, is important for the continued survival of populations, especially in the face of changing environments. Evolution is a change in allele frequencies in a population over time. Evolution can be adaptive or nonadaptive. Natural selection is an adaptive form of evolution. Mutation, genetic drift, and gene flow are nonadaptive forms of evolution. The founder effect is a type of genetic drift in which a small number of individuals establishes a new population in a new location, with reduced genetic diversity as a likely result. The bottleneck effect is a type of genetic drift that occurs when the size of a population is reduced, often by a natural disaster, and the genetic diversity of the remaining population is reduced. Inbreeding of closely related individuals may occur in small, isolated populations, posing a threat to the health of a species. Gene flow is the movement of alleles between different populations of the same species, often resulting in increased genetic diversity of a population. Genetic diversity can be assessed by using DNA sequences to determine allele frequency. The Hardy-Weinberg principle describes the frequency of alleles and genotypes in a nonevolving population. It can be used to detect evolutionary change in a population, and to calculate allele frequencies when at least one genotype frequency is known. According to the biological species concept, a species is a population of individuals that can interbreed to produce fertile offspring. Speciation can occur when gene pools are separated, gene flow is restricted, and populations diverge genetically over time.

What is a gene pool?

From a population genetics perspective, each distinct population of organisms—whether mice in Manhattan or elephants in Africa—has its own particular collection of alleles, which together constitute its gene pool. The total collection of alleles in a population. Within the gene pool, each allele is present in a certain proportion, or allele frequency, relative to the total number of alleles for that gene in the population. For example, if a particular allele for a gene is present 50 times out of a total of 1,000 alleles, its allele frequency is 0.05.

Summary Multiple types of evidence support the theory of evolution:

Homologous structures provide evidence for common ancestry, while analogous structures show that similar selective pressures can produce similar adaptations (beneficial features). Similarities and differences among biological molecules (e.g., in the DNA sequence of genes) can be used to determine species' relatedness. Biogeographical patterns provide clues about how species are related to each other. The fossil record, though incomplete, provides information about what species existed at particular times of Earth's history. Some populations, like those of microbes and some insects, evolve over relatively short time periods and can observed directly.

The combination of heavy antibiotic use, lots of sick patients, and close quarters makes hospitals a fertile environment for the emergence of resistant bugs.

In response, many hospitals have implemented measures to reduce infections.

What contributes to human skin color, and why is there so much variation in skin color among different populations?

More than a decade ago, Jablonski and her husband, George Chaplin, a geographer, set out to understand why human populations evolved varying skin tones. They knew that skin tone largely reflects the amount of melanin, a pigment present in the skin. People naturally produce different levels of melanin. More melanin yields darker skin, less melanin yields lighter skin. Skin also responds to sunlight by producing more melanin and temporarily becoming darker Jablonski and Chaplin also knew that, in general, skin tone correlates with geography: people from regions closer to Earth's poles tend to be lighter-skinned and those from areas closer to the equator tend to have darker skin.

What can genetics and the fossil record tell us about human evolution?

Interestingly, the tree Wilson generated had two major branches: one that leads to individuals now living in all five of the regions studied—Asia, Australia, Europe, New Guinea, and Africa—and one that leads only to modern-day Africans. The mtDNA of people on the exclusively African branch had acquired twice as many mutations as the mtDNA of people on the rest of the tree. The most likely interpretation of these data, the scientists reasoned, was that the African mtDNA had had more time to accumulate mutations, and was consequently older, evolutionarily speaking. This would mean that humans originated in Africa, where they likely formed several ancestral populations. After some period of time, one group of Africans left the continent, and their descendants continued to migrate to other continents, eventually becoming the ancestors of modern-day Asians, Australians, and Europeans. Evidence suggests this migration began around 70,000 years ago. Since Wilson's study, additional evidence continues to back the out-of-Africa hypothesis. Fossils discovered in Ethiopia in 2003 and 2005 represent the oldest known fossils of modern humans, and they are 160,000 and 195,000 years old, respectively. Both sets of remains date precisely from the time Wilson and his colleagues think that Mitochondrial Eve lived in eastern Africa. The fossil discoveries provide evidence that anatomically modern humans were living in that region around the same time that Mitochondrial Eve lived, and provide further evidence that modern humans originated in Africa. Humans are grouped with the great apes because fossil evidence shows that modern humans and other present-day great apes evolved from a common ancestor that lived 13 million years ago. Of the living members of this group, humans and chimpanzees are the most closely related, although it has been about 7 million years since their last shared ancestor lived. During those 7 million years, both humans and chimps have undergone a tremendous amount of evolutionary change, which is why living humans look and behave so differently from chimps—or any other primate species living today. Scientists haven't yet discovered fossil remains of the last common ancestor of chimps and humans. However, in October 2009 the first analyses of fossil remains of a 4.4-million-year-old hominid, Ardipithecus ramidus, nicknamed Ardi, were published. Ardi's remains are among the oldest hominid fossils so far discovered and, as such, give tantalizing clues to early human origins.

"Every one of us has probably had a staph infection at some point," explains Daum. "Staph ranges from the commonest cause of infected fingernails all the way to a severe syndrome with rapid death, and everything in between.

Most staph infections don't even result in a medical encounter." Staph bacteria can cause such a range of symptoms in part because there are many different strains of staph. Each strain differs from all others in its genetic makeup.

How do populations evolve, and what is the role of evolution in antibiotic resistance?

Mutations aren't the only way that populations of bacteria can acquire genetic variation. Bacteria can acquire new alleles, and even new genes, through a mechanism called gene transfer, in which pieces of DNA pass from one type of bacteria to another An entire population of organisms with a new trait can arise only when the environment favors that trait—that is, when the trait is advantageous to the organisms carrying it. When a population's environment favors one trait over others, the frequency of alleles that code for that trait in the population changes over time. The surviving bacteria reproduce and pass their alleles for drug resistance on to future generations. Consequently, the frequency of the resistance trait increases. This is how a population evolves. An organism's ability to survive and reproduce in a particular environment is called its fitness. The higher an organism's fitness, the more likely that alleles carried by that organism will be passed on to future generations and increase in frequency. In an environment in which antibiotics are abundant, drug-resistant bacteria are fitter than nonresistant bacteria

GENETIC DRIFT. FOUNDER EFFECT BOTTLENECK EFFECT

Random changes in the allele frequencies of a population between generations; genetic drift tends to have more dramatic effects in smaller populations than in larger ones A type of genetic drift in which a small number of individuals leaves one population and establishes a new population, resulting in lower genetic diversity than in the original population. A type of genetic drift that occurs when a population is suddenly reduced to a small number of individuals, and as a result alleles are lost from the population.

What is staph, and can a person have it in the absence of an infection? MRSA infection is caused by the bacterium --—often called simply "staph. an ---bacterium become widespread in recent years and which is difficult to treat with many existing antibiotics. Although all strains of staph can cause infection, the medical community is especially concerned about ----strains that have developed resistance to the antibiotic drugs that once effectively killed them. "MRSA" is actually a ----because the antibiotic methicillin is no longer used to treat staph infections. Drug-resistant strains of staph are usually resistant to several different types of antibiotics, including penicillins and cephalosporins. Surprisingly, staph bacteria cause no harm to most of the people who carry them. About one-third of the U.S. population carries staph on their ---or in their nose, and about 2% of the population carries MRSA, according to the Centers for Disease Control and Prevention (CDC). If you carry staph of any strain but aren't sick, you are "----" but not infected. Staph spreads from person to person through skin-to-skin contact or through shared contaminated items such as towels and bars of soap. Most healthy people can be colonized with any staph strain, including MRSA, and not become ill—for the most part our ----protect us. But infections can occur if staph bacteria come into contact with a wound or otherwise enter the body. For example, athletes who have cuts and scrapes may acquire a staph infection in locker rooms or during contact sports. Staph infection usually causes only minor skin eruptions such as boils or pustules that can resemble spider bites. But if staph manages to enter the ----or travel deeper into the body—becoming invasive—then more serious complications can occur

Staphylococcus aureas infectious S. aureus misnomer skin colonized skin and our immune systems bloodstream

Staph Colonization and Infection

Staphylococcus aureas is a spherical bacterium that cause pimples, boils, wound infection. S. aureus can be passed from person to person by direct contact with contaminated skin or by transfer of the bacteria via contaminated objects or surfaces

The Hard-Weinberg Law: The Hardy-Weinberg LawAssumptions: HWE---Predictions:

The genotype frequencies andgene frequencies of a large, randomly mating populationremain constant provided immigration; mutation andselection do not take place. • Population is infinitely large • Mating is random • No natural selection • No mutation. • No migration. * Allele frequencies do not change over generations.*Genotype frequencies can be predicted from alleles• At equilibration: p2 + 2pq + q2 = 1o p = allelic frequency of Ao q = allelic frequency of ao p2 frequency of AAo 2pq frequency of Aao q2 frequency of aa

GENE FLOW INBREEDING Mating INBREEDING DEPRESSION

The movement of alleles from one population to another, which may increase the genetic diversity of a population. between closely related individuals. Inbreeding does not change the allele frequency within a population, but it does increase the proportion of homozygous individuals to heterozygotes The negative reproductive consequences for a population associated with having a high frequency of homozygous individuals possessing harmful recessive alleles.

HARDY-WEINBERG PRINCIPLE BIOLOGICAL SPECIES CONCEPT REPRODUCTIVE ISOLATION SPECIATION

The principle that, in a nonevolving population, both allele and genotype frequencies remain constant from one generation to the next. The definition of a species as a population whose members can interbreed to produce fertile offspring. Mechanisms that prevent mating (and therefore gene flow) between members of different species. The genetic divergence of populations, leading over time to reproductive isolation and the formation of new species.

ADAPTATION DIRECTIONAL SELECTION STABILIZING SELECTION DIVERSIFYING SELECTION

The process by which populations become better suited to their environment as a result of natural selection. A type of natural selection in which organisms with phenotypes at one end of a spectrum are favored by the environment. A type of natural selection in which organisms near the middle of the phenotypic range of variation are favored by the environment. A type of natural selection in which organisms with phenotypes at both extremes of the phenotypic range are favored by the environment.

Why does genetic diversity matter?

You can think of a gene pool as being like a population's portfolio of financial assets. Having a diverse array of investments is a better strategy for long-term success than having all your money tied up in one kind of stock—especially if that stock loses value in changed economic times.

The Human Body Hosts a Huge Numberof Bacteria

a huge diversity of microbes is found in and on the human body. thees resident bacteria are essential to human health. they can help block pathogens from establishing an infection, and many produce helpful components such as vitamins. in some cases, potential pathogens can also take up residence and cause disease if they can outgrow the other resident bacteria

ancomycin, a non-beta-lactam drug, is the antibiotic of choice when a serious MRSA infection is confirmed. But

even vancomycin isn't always effective; there are now staph strains resistant to vancomycin, too.

She found her first clue in a 1978 study showing that, in light-skinned people, an hour of intense sunlight can halve the level of an important vitamin called ---. Folate, also known as ---, is an essential nutrient, necessary for basic cellular processes like DNA replication and cell division. Then, at a seminar, Jablonski learned that low folate levels can cause severe birth defects such as spina bifida, a condition in which the spinal column does not close, and anencephaly, the absence at birth of all or most of the brain Jablonski considered a hypothesis first proposed in the 1960s by biochemist W. Farnsworth Loomis, who suggested that ----might play a role in the evolution of skin color. Unlike folate, which is destroyed by excess sunlight, the production of vitamin D requires ultraviolet light. Vitamin D is crucial for good health: it helps the body absorb calcium and deposit it in bones. During pregnancy women need extra vitamin D to nourish the growing embryo. And because vitamin D is so important for healthy bone growth, too little might cause bone distortion, and a distorted pelvis would make it difficult for a woman to bear children The researchers now had a complete hypothesis: light skin provided an evolutionary advantage in sun-poor parts of the world because it helped the body produce vitamin D, while dark skin was favored in sunny regions because it helped protect the body's folate stores. The body's need to balance levels of these two important nutrients given varied levels of UV light explains why there is so much variation in skin tone around the globe

folate folic acid vitamin D

which mechanism (mutation or gene transfer) is more likely to introduce a new allele, rather than a new gene, into the population?

mutation

A college wrestler has developed a serious (invasive) MRSA infection. List three possible sources of the MRSA bacteria causing his infection.

skin, nose, throat 1/3 of U.S. pop (nearly 90 mill peeps) is colonized by S. aureus. these bacteria do not usually cause illness unless they penetrate skin barriers through open hair follicles, cuts, scrapes

Development helps us solve other evolutionary conundrums as well, such as why reptiles like snakes don't have limbs like other tetrapods. In fact, snake embryos do possess the beginnings of limbs, but these limb buds remain rudimentary and do not develop into full-fledged limbs (although you can still see stubby hindlimbs in some species of snake today). Such ---structures, which serve no apparent function in a modern organism, are strong evidence for evolution: these now apparently useless features are inherited from an ancestor in whom they did serve a function. Other examples of vestigial structures include the human tailbone and the phenomenon of "goose pimples"

vestigial

Once a population has lost genetic diversity because of genetic drift, there are only two ways that genetic diversity can be reintroduced: Like genetic drift, gene flow is a type of ---evolution that does not lead to a population becoming more adapted to its environment. Unlike genetic drift, gene flow tends to increase the genetic diversity of a population, not decrease it

(1) by mutation, which as we saw in Chapter 10 continually introduces new alleles into the population, and (2) by gene flow, in which alleles move between populations as individuals leave and enter populations and breed with members of other populations. nonadaptive

Species Are Reproductively Isolated

- ecological isolation -Ecological, or habitat, isolation occurs when two species that could interbreed do not because the species live in different areas. For example, in India both the lion and tiger exist and are capable of interbreeding; however, the lion lives in the grasslands and the tiger lives in the forest. Temporal Isolation - Temporal isolation is when species that could interbreed do not because the different species breed at different times. This temporal difference could occur at difference times of day, different times of the year, or anything in between. Behavioral Isolation - refers to the fact that many species perform different mating rituals. This is a common barrier between animals. For example, certain species of crickets will only mate with males that produce a particular mating song. Mechanical or Chemical Isolation - Mechanical isolation is caused by structures or chemical barriers that keep species isolated from one another. For example, in flowering plants, the shape of the flower will tend to match up with a natural pollinator. Plants that do not have the correct shape for the pollinator will not receive a pollen transfer. Likewise, certain chemical barriers prevent gametes from forming. Gametic Isolation - a type of prezygotic barrier. Gametic isolation happens when the egg and sperm are released but a zygote is not formed. A zygote is the cell produced when an egg and sperm unite. The term 'gamete' refers to the reproductive cells like eggs and sperm. the animals do come into contact, but the gametes (reproductive cells) are not compatible. Hybrid Infertility- offspring are viable but cannot reproduce Hybrid inviability - species' gametes unite but viable offspring cannot form.

How do bacteria resist the effects of antibiotics?

-Bacteria can acquire mutations when their DNA replicates. The random mutations cause changes in alleles in the population, which can lead to antibiotic resistant bacteria. _Can also acquire new alleles, and new genes through a mechanism called gene transfer, in which pieces of DNA pass from one type of bacteria to another.

An Organism's Fitness Depends on Its Environment In the absence of antibiotics, is there a difference between the fitness of antibiotic-sensitive and antibiotic-resistant variants?

-determined by interactions btw phenotype and environment, antibiotic-resistant bacteria, for ex, have a high fitness in the presence of antibi -The abundance of antibiotics in the environment has created the perfect breeding ground for antibiotic-resistant staph. In a different environment, however, one in which antibiotics are less common, these same resistant bacteria will not necessarily have an edge over other bacteria. In other words, fitness is always relative to the environment; organisms can be fit in one environment and not in another. no

Evidence for Change quiz 1 Which of the following organisms would be most "fit"? 2 Which of the following statements about fossilization is false? 3 When paleontologists find fossils, generally the further down they are buried... 4 Bats are closely related to rodents and probably evolved from something like a mouse. A bat's wing and a butterfly's wing are then examples of: 5 Bats are closely related to rodents and probably evolved from something like a mouse. A bat's wing and a bird's wing are then examples of:

1 An organism that is brightly colored and is attractive to mates leading to lots of offspring that also reproduce 2 The fossil record should show a complete record of evolution on earth. 3 The older they are 4 Convergent evolution 5 Homologous structures

Pathogens quiz 1 Which of the following is not an example of a functional trait of living organisms? 2 Movement across a membrane that does not require energy and does not require a protein is called: 3 Which of the following organelles are found in both plants and animals? 4 Which of the following is an important characteristic of the cell membrane? 5 A molecule which interacts well with water (water loving) is called a(n) _______ substance? 6 The primary lipid found in cell membranes is 7 Cell theory states that 8 A distinguishing feature of eukaryotic cells is that they 9 Your roommate is getting over a strep infection and you start getting a sore throat. What should you do? 10 On Saturday you were at an TXST football game when the temperature dropped and it started raining. Monday your nose is plugged up 11 Ten years from now your baby is running a fever of 100 F, but otherwise seems OK. What should you do? 12 There is no way you can the smallpox disease from the smallpox vaccine. 13 It is a bad idea to re-wash bagged spinach or bagged salad mixes. 14 Which of the following statements about cell theory is false?

1 Obtain and use energy from the sun 2 Simple diffusion 3 Ribosomes and Mitochondria 4 -It keeps molecules out of the cell. -It keeps molecules in the cell. -It is formed by a phospholipid bilayer. -It defines the boundary between what is "inside" and "outside" the cell. 5 Hydrophilic 6 phospholipids. 7 all living things are composed of cells. and cells come from other cells. 8 contain a nucleus and other organelles. 9 Go to the doctor 10 False 11 Nothing, but watch him carefully 12 True 13 True 14 Bacteria are not considered living because they do not possess membrane-bound organelles.

1 Which of the following is most likely to leave a fossil that represents most of the organism? a- a jellyfish b- a worm c- a wolf d- an octopus (an organism that lacks a skeleton) e- All of the above are equally likely to leave a fossil. 2 Generally speaking, if you are looking at layers of rock, at what level would you expect to find the newest—that is, the youngest—fossils? 3 You are examining a column of soil that contains vertebrate fossils from deeper to shallower layers. Would you expect a fossil with four limbs with digits to occur higher or lower in the soil column relative to a "standard" fish? Explain your answer. 4 What can the fossil shown below tell us about the structure and lifestyle of the organism that left it? Describe your observations.

1 c- a wolf 2 The newest fossils will be in the layers closest to the surface. 3 A fossil with four limbs and digits would be the fossil of a more recent organism than a "standard" fish. Thus, the "standard" fish fossil would be in deeper layers above that fish fossil. 4 This fossil seems to be similar to modern-day bony fishes. It is possible to observe fins with rays, suggesting that this organism was aquatic and able to swim. There does not appear to be a distinct neck, consistent with a fish, and there could be a gill cover present, again consistent with an aquatic organism. This may have been a predatory fish, as there appear to be teeth present.

1 Genetic diversity is measured in terms of allele frequencies (the relative proportions of specific alleles in a gene pool). A population of 3,200 mice has 4,200 dominant G alleles and 2,200 recessive g alleles. What is the frequency of g alleles in the population? 2. From this information, which population is most likely to be an isolated population? Note that this gene has seven possible alleles: A1, A2, A3, a1, a2, a3, and a4. Population A: 30% A1, 30% a1, and 40% a4 Population B: 25% A2, 25% A3, 25% a2, 25% a3 Population C: 20% A2, 20% A3, 30% a2, 30% a3

1 g= .34 or 34% Total alleles is 6,400. Then divide g by total.2,200/6,400 2 Population A because it is less diverse so there are only 2 alleles

Preventing and treating infection by antibiotic resistant bacteria

1 reduce anabiotic's in livestock feed 2 keep locker rooms in sport equipment clean 3 wash hands frequently 4 research new vaccine 5 do not take antibiotics for viral infections

1 Can S. aureus be present in or on a person who has no evidence of an infection? 2 The term "MRSA" as it is used today refers to 3 What is the difference between an S. aureus colonization and an S. aureus infection? 4 MRSA is most likely to be problematic if found

1 yes; S. aureus is a common skin bacterium 2 S. aureus bacteria that are resistant to many antibiotics. 3 In colonization, the bacteria are growing on or in the body without causing disease. Infections are associated with disease. 4 in the bloodstream.

1 What types of evidence to scientists use to support their understanding of changes over time? 2 How do scientists interpret the fossil record? 3 How old is the earth, and how do we know? 4 What evidence have we gathered from ice fish? 5 What are the differences between Homology, Vestigial Structures, and Convergent Evolution?

1- paleontology, geology, genetics and developmental biology. AND fossils, DNA, homology, vestigial structures 2- Fossils are important evidence for evolution because they show that life on earth was once different from life found on earth today. ... Paleontologists can determine the age of fossils using methods like radiometric dating and categorize them to determine the evolutionary relationships between organisms. 3- By dating the rocks in Earth's ever-changing crust, as well as the rocks in Earth's neighbors, such as the moon and visiting meteorites, scientists have calculated that Earth is 4.54 billion years old, with an error range of 50 million years. 4- DNA 5- -In homology, the homologous structures did, in fact, evolve from a recent common ancestor. Organisms with homologous structures are more closely related to each other on the tree of life than those with analogous structures. -However, they are still closely related to a recent common ancestor and have most likely undergone divergent evolution. -Vestigial structures are various cells, tissues, and organs in a body which no longer serve a function. A vestigial structure can arise due to a mutation in the genome. This mutation will cause a change in the proteins that are required for the formation of the structure. -convergent evolution: a trait of evolution in which species not of similar recent origin acquire similar properties due to natural selection -Analogy, or analogous structures, is actually the one that does not indicate there is a recent common ancestor between two organisms. Even though the anatomical structures being studied look similar and maybe even perform the same functions, they are actually a product of convergent evolution

11 Rank the levels of genetic diversity you would expect to find within the five populations listed in Question 11 from highest to lowest. Justify your ranking. 12 If there were many human females living ~200,000 years ago, why do we find that the mitochondrial DNA in all living humans is all related to a single woman from that time? What kind of evidence could you look for to test your explanation? (Hint: Think about all the human fossils that have been uncovered, and consider that it is possible to extract DNA from fossils.)

11 12 If you trace back the DNA in the maternally inherited mitochondria within our cells, all humans have a theoretical common ancestor. This woman, known as "mitochondrial Eve", lived between 100,000 and 200,000 years ago in southern Africa. She was not the first human, but every other female lineage eventually had no female offspring, failing to pass on their mitochondrial DNA. As a result, all humans today can trace their mitochondrial DNA back to her. Within her DNA, and that of her peers, existed almost all the genetic variation we see in contemporary humans. Since Eve's time, different populations of humans have drifted apart genetically, forming the distinct ethnic groups we see today. Read more: https://www.newscientist.com/article/mg22429904-500-found-closest-link-to-eve-our-universal-ancestor/#ixzz6lW507My6

11 What are the two major mechanisms by which bacterial populations generate genetic diversity? 12 What is the environmental pressure in the case of antibiotic resistance? 13 What is the evolutionary meaning of the term "fitness"? 14 The evolution of antibiotic resistance is an example of

11 gene transfer and mutation 12 the presence or absence of antibiotics in the environment 13 The ability of an individual to survive and reproduce in a given environment. Individuals that are more fit leave more offspring and more of their alleles in the next generation relative to individuals that are less fit. 14 directional selection.

7 In the presence of penicillin a) What happens to a penicillin-sensitive strain of S. aureus? b) What happens to a penicillin-resistant strain of S. aureus? 8 How do beta-lactam antibiotics kill sensitive bacteria? 9 Why do beta-lactam antibiotics affect sensitive bacterial cells but not eukaryotic cells? (You may want to review cell structure, 10 A sensitive S. aureus bacterium acquires a new gene that allows it to resist the effects of beta-lactam antibiotics (that is, the bacterium is now resistant). What might the protein encoded by that gene do?

7 a) A sensitive strain of S. aureus will eventually burst (lyse) and die because of its weakened cell wall. b) Penicillin would be ineffective and the bacteria would continue to thrive and grow. 8 by destabilizing the cell wall 9 Beta-lactam antibiotics interfere with the synthesis of peptidoglycan-containing cell walls. Humans (and other animals) do not have cell walls at all, and while plant cells do have a cell wall, it is made of cellulose and not peptidoglycan. Eukaryotic cells therefore do not have the structure that is the target of penicillin (and other beta-lactam antibiotics). 10 digest beta-lactam antibiotics

13 Compare and contrast the structure and function of an eagle wing with the structure and function of a human arm. 14 Vertebrate embryos have structures called pharyngeal pouches. What do these structures develop into in an adult human? In an adult bony fish? 15 You have three sequences of a given gene from three different organisms. How could you determine how closely the three organisms are related? 16 What is the evolutionary explanation for the fact that both human hands and otter paws have five digits?

13 The skeletal anatomy of an eagle wind and that of a human arm are very similar. All major bones are present in each, and in the same locations relative to other bones. In the human, the most distal bones, like the tips of digits, are longer and arranged in a way that permits fine manipulation of objects with hands and fingers. Birds do not need to carry out this fine-scale manipulation, as their wings are specialized for flying. 14 middle ear bones in humans; gills in adult bony fish 15 You could make pairwise comparisons between the sequences, counting the number of nucleotide differences between them. The more differences there are, the less similar the sequences are. More-similar sequences suggest closer relationships, and less-similar sequences suggest more distant relationships. Ideally, you would compare a large number of genes before coming to a conclusion. 16 Humans and otters share a common ancestor, and therefore homologous bone structures, including five digits on the hands. Both humans and otters are dexterous with their hands, using them for a variety of important functions, so the continued presence of five digits would have been selected for over evolutionary time.

14 Which of the following statements is/are true about a nonevolving population? 15 A starting population of bacteria has two alleles of the TUB gene, T and t. The frequency of T is 0.8 and the frequency of t is 0.2. The local environment undergoes an elevated temperature for many generations of bacterial reproduction. After 50 generations of reproduction at the elevated temperature, the frequency of T is 0.4 and the frequency of t is 0.6. Has evolution occurred? Explain your answer. 16 Why is inbreeding detrimental to a population?

14 Allele frequencies do not change over generations. Genotype frequencies do not change over time. Individuals choose mates with which they share many alleles 15 Yes, evolution has occurred. The genetic definition of evolution is a change in the allele frequencies within a population 16 Inbreeding is detrimental because it decreases the number of heterozygotes in a population, increasing the proportion of individuals which are homozygous for recessive alleles. Many recessive alleles are mutations that are detrimental but which do not confer a phenotype in heterozygous individuals because the non mutated gene is a dominant allele; however, in a homozygous recessive individuals, these traits are expressed usually with extremely negative consequence including decreased fitness, fertility, or viability. this phenomenon is called inbreeding depression

15 What percentage of DNA sequences do all humans share? 16 Of the following traits that are associated with being human, which evolved most recently? 17 Place the following ancestors in order of earliest (1) to most recent (5). ______Homo sapiens ______Last common ancestor of chimpanzees and humans ______Australopithecus ______Ardipithecus ramidus ______Homo erectus 18 Why is there so much variation in human skin coloration?

15 >99% 16 big brain 17 Last common ancestor of chimpanzees and humans. Ardipithecus ramidus Australopithecus homo Erectus homo sapiens 18 This occurred because humans underwent natural selection that resulted in traits that conferred advantages to humans becoming fixed in populations.This occurred because skin coloration results in different advantages depending on the levels of sun in the region.This occurred because alleles that are harmful in one environmental context may be beneficial in another.This occurred because humans are found in areas that range from high-UV-light environments to low-UV-light environments.

15 In humans, very-large-birth-weight babies and very tiny babies do not survive as well as midrange babies. What kind of selection is acting on human birth weight? 16 Binary fission is asexual. What does this mean? How could two daughter cells end up with different genomes at the end of one round of binary fission? 17 In what sense do bacteria "evolve faster" than other species?

15 stabilizing selection 16 Asexual reproduction involves only one parent. That parent passes on a copy of all of its genetic material to its offspring. This means that the offspring are copies of the parent. The two daughter cells that are the products of binary fission could be genetically different if a mutation occurred during replication of the parent genome before division. One copy of the genome would contain the mutation and one copy would not, and each daughter cell would inherit one of the two different copies. 17 Because bacteria divide very rapidly, they have a very short generation time. As evolution is a change in allele frequency over time, it doesn't take long for bacterial populations to accumulate many generations. As there is a chance of one or more mutations to arise with every generation, there is a wealth of genetic diversity for natural selection to act on.

17 Could you use the presence of a tail to distinguish a human embryo from a chicken embryo? Why or why not? 18 If, in humans, the DNA sequence TTTCTAGGAATA encodes the amino acid sequence phenylalanine-leucine-glycine-isoleucine, what amino acid sequence will that same DNA sequence specify in bacteria? 19 Gene X is present in yeast and in sea urchins. Both produce protein X, but the yeast protein is slightly different from the sea urchin protein. What explains this difference? How might you use this information to judge whether humans are closer evolutionarily to yeast or to sea urchins?

17 At early stages of development, both human and chicken embryos have a tail, so this feature will not allow you to distinguish between an early human embryo and an early chicken embryo. 18 As the genetic code is universal (with only a few exceptions), the same DNA sequence will encode the same amino acid sequence in both humans and bacteria. 19 Both proteins are encoded by gene X in each organism. The fact that the amino acid sequences differ between sea urchin and yeast means that the gene sequence of gene X differs between sea urchins and yeast. This is because sea urchins and yeast have each acquired mutations (that is, nucleotide changes) in the gene since they diverged from their last common ancestor. The greater the number of nucleotide differences, the longer it has been since the organisms split from their common ancestor, and the less closely they are related. The sequence of gene X from humans could be compared to the sequence from sea urchins and yeast, and the number of nucleotide differences could be used to establish relationships.

18 A single S. aureus cell gets into a wound on your foot. S. aureus divides by binary fission approximately once every 30 minutes. 2^n Thirty minutes after the initial infection, how many S. aureus cells will be present? In 1 hour, how many S. aureus cells will be present? In 12 hours, how many S. aureus cells will be present? (Hint: The general formula is 2number of generations; you need to figure out how many generations occurred in 12 hours.) (12+12=24) Mutations occur at a rate of 1 per 1010 base pairs per generation. S. aureus has 2.8 × 106 base pairs in its genome. Therefore, approximately 0.0028 mutations will occur per cell in the population. At the end of 12 hours, how many mutations will be present in the population of S. aureus in the wound in your

18 2 4 16,777,216 At the end of 12 hours, 0.0028 x 16,777,216 = 46,976 new mutations will be present.

18 The biological species concept defines a species 19 How does geographic isolation contribute to speciation? 20 Two populations of rodents have been physically separated by a large lake for many generations. The shore on one side of the lake is drier and has very different vegetation from that on the other side. The lake is drained by humans to irrigate crops, and now the rodent populations are reunited. How could you assess if they are still members of the same species? 21 If geographically dispersed groups of a given species all converge at a common location during breeding season, then return to their home sites to bear and rear their young, what might happen to the gene pools of the different groups over time?

18 on the basis of the ability to mate and produce fertile offspring. 19 by making it more difficult for members of the species to locate each other. 20 According to the biological species concept, if members of different populations can successfully reproduce (and produce fertile offspring), then they are members of the same species. If they cannot mate or produce fertile offspring after their isolation, then they have (by definition) become different species. 21 While each population may live in a separate region, the fact they converge during breeding season means that alleles will be exchanged and shared throughout all the populations. They are not geographically isolated (at least at a genetic level).

19 If we take the fittest bacterium from one environment—one in which the antibiotic amoxicillin is abundant, for example—and place it in an environment in which a different antibiotic is abundant, will it retain its high degree of fitness?

19 not necessarily; fitness depends on the ability of an organism to survive and reproduce, and it may not do this as well in a different environment

20 The gene responsible for hairlessness in Mexican hairless dogs is called corneodesmosin (CDSN). This gene is present in other organisms. Look at the sequence of a portion of the CDSN gene from pairs of different species, given below. For each pair, determine the number of differences. From the variations in this sequence, which organism appears to be most closely related to humans? Which organism appears to be least closely related to humans? 21 how do pop evolve?

20 chimpanzees are most closely related to humans and the organism that is least closely related to humans is the dog 21 isolation+ diff environmental pressures = new types

26 Low folate can cause defects in? 27 how does lighter skin come about? 28 Which line of evidence supports the conclusion that the common ancestor of modern chimps humans lived around 7 million years ago? 29 On the evolutionary tree of humans, which lineage is the oldest? 30 Which remains are the oldest hominid fossils discovered so far? 31 Let's pretend that UVB exposure occurs at the highest levels at the poles, and at the lowest levels at the equator. In this alternate planet Earth, where would you expect to find fair-skinned humans? 32 Scientists have studied patterns of mitochondrial DNA to determine where humans first evolved and how they spread. Humans inherit their mitochondrial genes only from their mothers. Why aren't a father's mitochondrial genes passed to his offspring? 33 What are characteristics of mitochondrial DNA that made it a suitable choice for studying human evolutionary patterns? 34 What evidence supports the idea that Australopithecines could walk upright and did not live in trees? 35 According to the "Out of Africa" hypothesis of human origins and migration, which population would have the lowest level of genetic diversity?

26 -DNA replication -cell division -birth defects like spina bifida 27 Lighter skin = less melanin to absorb UV light= more folate destroyed 28 Analysis of protein and DNA sequences suggests a divergence 7 million years ago. 29 Australopithecus africanus 30 Ardipithecus ramidus 31 around the equator 32 Sperm do not contribute their mitochondria to the zygote. 33 -Mitochondrial DNA mutates at a fairly regular rate.-Individuals with nearly identical mtDNA sequences are more closely related.-Mutations from mothers are passed to offspring without recombination with paternal mtDNA. 34 their skeletons and lack of an opposable big toe 35 South Americans

3 A small population of 26 individuals has five alleles, A through E, for a particular gene. The E allele is represented only in one, homozygous, individual: Five individuals are D/A heterozygotes. Five individuals are A/A homozygotes. Five individuals are A/B heterozygotes. Five individuals are C/D heterozygotes. Five individuals are C/C homozygotes. One individual is an E/E homozygote. Added = 26 a) Calculate the allele frequency of each of the five alleles. b) Five A/E heterozygotes migrate into the population. Now what are the allele frequencies of each of the five alleles in the population?

3= In the original population, there are 26 individuals and 52 alleles of the gene in question (26 + 26= 52). The allele frequencies are: (5 +5) = 10/52 = 0.19 D; (5+5+5+5) 20/52 = 0.38 A; 5/52 =0.20 B; 15/52 = 0.29 C; 2/52 = 0.04 E. After the migration, (Five A/E heterozygotes) the allele frequencies are: (26+5 = 31 then 31 +31= 62) 10/62 = 0.16 D; 25/62 = 0.4 A; - b/c 5 were added 5/62 = 0.08 B; 15/62 = 0.24 C; 7/62= 0.12 E. The frequency of E increases substantially.

4 Some populations, for example cheetahs, have gene pools with very few different alleles. What approach(es) could be taken to try and introduce new alleles into these kinds of populations? 5 The global human population continues to grow, and more people than ever are living in crowded cities. Given this situation, what selective pressures might the human population be currently facing or be expected to face in the near future?

4 A common approach is to find distinct species or populations that will successfully interbreed with the cheetahs. If interbreeding with distantly related species or populations is successful, then new alleles will be introduced into the population. 5 There are many possibilities. Some of these include the pressure of infectious diseases (which can spread easily in crowded populations), and the pressure of stress (associated with living in crowded cities). If city dwellers do not spend much time outside, there may be pressures associated with low exposure to sunlight. There may also be pressures exerted by air pollution.

5 An athlete has a nasty skin infection caused by MRSA. How might this infection have been contracted? 6 For the patient in Question 5, which general kinds of antibiotics would you choose (or avoid) in treating the infection? What other measures would you recommend to prevent spread of MRSA to the athlete's teammates and family? Explain your answer.

5 The athlete could have been exposed by direct skin contact with another athlete who has MRSA, or by coming into contact with a contaminated item (e.g., towels, shared sports equipment), particularly if the contact occurs at sites where the skin is broken, as by a scrape or cut. 6 -Vancomycin continues to be the drug of choice for treating most MRSA infections caused by multi-drug resistant strains. Clindamycin, co-trimoxazole, fluoroquinolones or minocycline may be useful when patients do not have life-threatening infections caused by strains susceptible to these agents. - avoid methicillin, amoxicillin, penicillin, oxacillin, and other common antibiotics known as cephalosporins. -Use Contact Precautions when caring for patients with MRSA (colonized, or carrying, and infected). Contact Precautions mean: Whenever possible, patients with MRSA will have a single room or will share a room only with someone else who also has MRSA.

5 You have molecular evidence that leads you to hypothesize that a particular group of soft-bodied sea cucumbers evolved at a certain time. You have found a fossil bed with many hard-shelled mollusks dating from the critical time, but no fossil evidence to support your hypothesis about the sea cucumbers. Does this cause you to reject your hypothesis? Why or why not? 6 A specific type of oyster is found in North American fossil beds dated from 100 million years ago. If similar oyster fossils are found in European rock, in layers along with a novel type of barnacle fossil, what can be concluded about the age of the barnacles? Explain your answer. 8 Which of the following features of Tiktaalik is not shared with other bony fishes?

5 The hypothesis should not be rejected because of the absence of sea cucumber fossils from the fossil bed. Soft-bodied organisms (such as sea cucumbers) do not fossilize well, and so do not leave fossils in the fossil record. 6 As the oysters date from 100 million years ago, and the barnacles are found in the same layers as the oysters, the barnacles must be at least 100 million years old. 8 c. a mobile neck

9 Tiktaalik fossils have both fishlike and tetrapod-like characteristics. Which characteristics are related to supporting the body out of the water? 10 Tiktaalik fossils are described as "intermediate" or "transitional" fossils. What does this mean? Why are transitional organisms significant in the history of life? 11 Tiktaalik has been called a "fishapod"—part fish, part tetrapod. Speculate on the fossil appearance of its first true tetrapod descendant—what features would distinguish it from Titkaalik? How old would you expect those fossils to be relative to Titkaalik? 12 If some fish evolved modifications that allowed them to be successful on land, why didn't fish just disappear? In other words, why are there still plenty of fish in the sea if the land presented so many favorable opportunities?

9 Long and sturdy ribs (to help support the body) and pectoral fins that have wrists and can bear weight. 10 Transitional fossils are "intermediate" in that they are midpoints between two groups of organisms. They are important because they shed light on how groups of organisms were able to move into new habitats or develop new structures. Titkaalik represents the transition between aquatic bony fishes and land-dwelling tetrapods. 11 The first real tetrapod would likely have fully developed forelimbs and hind limbs, both of which would have jointed wrists and ankles and could bear weight. These fossils might also have more distinct jointed digits (both fingers and toes). These fossils would be younger (that is, more recent) than the Titkaalik fossils, as true tetrapods would be the descendents of Titkaalik. 12 While land represented a new opportunity, the oceans, lakes, rivers and streams still provided many opportunities for survival and reproduction, and fish that were well adapted to this environment continued to leave descendants.

MELANIN FOLATE VITAMIN D MITOCHONDRIAL DNA (mtDNA) HOMINIDS

A pigment produced by a specific type of skin cell that gives skin its color. A B vitamin also known as folic acid; folate is an essential nutrient, necessary for basic cellular processes such as DNA replication and cell division. A fat-soluble vitamin required to maintain a healthy immune system and to build healthy bones and teeth. The human body produces vitamin D when skin is exposed to UV light. The DNA within mitochondria; it is inherited solely from the mother. Any living or extinct member of the family Hominidae, the great apes—humans, orangutans, gorillas, chimpanzees, and bonobos

VERTEBRATE DESCENT WITH MODIFICATION FOSSILS FOSSIL RECORD VESTIGIAL STRUCTURE

An animal with a bony or cartilaginous backbone. Darwin's term for evolution, combining the ideas that all living things are related and that organisms have changed over time. The preserved remains or impressions of once-living organisms. An assemblage of fossils arranged in order of age, providing evidence of changes in species over time. A structure inherited from an ancestor that no longer serves a clear function in the organism that possesses it.

In binary fission, a single parental cell simply replicates its single chromosome, grows, and then splits into two daughter cells, each with a copy of the parental DNA How Bacteria Reproduce

Bacteria reproduce through binary fusion. Binary fusion is a form of asexual reproduction in which a single parent cell replicates its contents and then divides into two daughter cells. each daughter cell inherits all its DNA from the single parent cell 1- cell elongates and DNA is replicated 2- cell wall and plasma membrane begins to divide \ 3- cross-wall forms completely around DNA 4- Daughter cell separates Because bacteria reproduce much more rapidly than other organisms—a generation of bacteria can double in as little as 20 minutes—they accumulate mutations at a relatively high rate. An entire population of bacteria that is genetically different from the original cell can arise very quickly. A population is a group of individuals of the same species (in this case Staphylococcus aureus) living together in the same geographic area. That area could be a prairie, a pond, or a person's nose. New mutations can spread throughout a population of bacteria in a person's body over the course of an illness.

CHAPTER 19 SUMMARY

Humans are 99.9% genetically identical to one another regardless of geographic origin. Biologically distinct human races do not exist. All humans are members of a single biological species, Homo sapiens, which evolved relatively recently—just 200,000 years ago. Physical features shared by people within populations reflect adaptations to specific environments. Alleles can be harmful, beneficial, or neutral in their effect on survival and reproduction. Skin color most likely evolved in response to environmental UV levels, an example of evolution by natural selection. Alleles for darker skin conferred an advantage in sunnier environments, while alleles for lighter skin conferred an advantage in regions that receive weak sunlight. Skin color represents an evolutionary trade-off between the need for vitamin D, which requires adequate sunlight for its production, and the need for folate, which is destroyed by too much sunlight. Fossil evidence shows that humans and apes descended from a common ancestor and that walking upright preceded development of a big brain. There were many species that could walk upright before Homo sapiens appeared. Fossil and DNA evidence shows that anatomically modern humans first emerged in Africa, approximately 200,000 years ago, and subsequently spread to other continents, beginning about 70,000 years ago. All modern-day humans can trace a portion of their genetic ancestry back to a single woman, Mitochondrial Eve, who lived 200,000 to 150,000 years ago in Africa. Humans evolved from apelike primate ancestors who likely had light skin. Darker skin emerged in tandem with loss of body hair as our hominid ancestors ventured into the hot savannah, while lighter skin emerged as humans migrated farther north.

By definition, a population is not evolving (and is therefore in Hardy-Weinberg equilibrium) when it has stable allele frequencies and stable genotype frequencies from generation to generation. This can be achieved only when all five of the following conditions are met:

No mutation introducing new alleles into the population No natural selection favoring some alleles over others An infinitely large population size (and therefore no genetic drift) No gene flow between populations Random mating of individuals

How does the gene pool of an evolving population compare to the gene pool of a nonevolving population?

One reason gene flow is important is that small, isolated populations can be damaged by lack of genetic diversity.

CHAPTER 13 SUMMARY

Populations are groups of individuals of the same species living together in the same geographic area. Populations of bacteria exist nearly everywhere, including on and in our bodies; most are harmless or even beneficial, but some can cause disease Within any population, there is genetic variation among individuals. This variation exists in the form of different alleles that arise randomly by mutation. Bacterial populations can acquire genetic variation by both mutation and gene transfer—the direct exchange of DNA between bacterial cells. Genetic variation in a population gives rise to corresponding phenotypic variation in the population. Individuals with different phenotypes will have differing ability to survive and reproduce in a population; that is, they will have different fitness. The differential survival and reproduction of individuals in a population over time in response to environmental pressure is called natural selection. Natural selection is one cause of evolution, which is defined as a change in the allele frequency of a population over time. Individuals with higher fitness in a given environment reproduce and pass on their alleles more frequently than do individuals with lower fitness, resulting in evolution by natural selection. Over time, natural selection leads to adaptation: advantageous traits become more common in the population, which as a result becomes more suited, or adapted, to its environment. Natural selection can take several forms that shift phenotypes in a population in distinct ways: directional selection, diversifying selection, or stabilizing selection. Antibiotic-resistant populations of bacteria emerge by directional selection in the presence of antibiotics.

---explains why species remain separate—as do the variety of ant species that share a median strip—but how did the species form in the first place? New species form when a strong barrier to ---occurs between populations. That barrier could be physical—like a road or river that divides a forest in two—or climatic, like the different temperatures that occur at different elevations on a mountainside. Once this barrier forms, the separated gene pools will evolve independently by the mechanisms we have already encountered: mutation, genetic drift, and natural selection. Eventually, if enough genetic changes accumulate between populations of the same species to make them reproductively isolated, the two populations may diverge into separate species, a process called ---. Speciation is happening all the time in nature, but it can be hard to see because it occurs so slowly.

Reproductive isolation gene flow speciation

methicillin-resistant ---(MRSA), which has become widespread in recent years and which is difficult to treat with many existing antibiotics. MRSA (pronounced "mer-sa") sickened some 75,000 people in the United States in 2012 and killed nearly 10,000. Formerly, outbreaks of MRSA were confined mainly to hospitals, where people are often very ill and have compromised immune systems Scientists are now seeing bacterial infections that don't respond to any known antibiotics, leading many to fear the day when we run out of treatment options alterm-19together.

Staphylococcus aureus

Which came first, a big brain or walking upright? Ardi provides the answer: Ardi had a small brain, suggesting that she could not use complex language. But Ardi's bones clearly show that she could walk upright without dragging her knuckles, while still able to maneuver on all fours in trees. === , most likely when our hominid ancestors began eating meat from large animals. The first hominid tool-users were members of the genus Australopithecus. This genus walked upright and appears to have lived on the ground, rather than in trees, as evidenced by the lack of an opposable big toe, which had helped the early hominids grip branches.

The ability to walk upright therefore evolved first and was a major step toward becoming human.

How do new species arise, and how can we recognize them?

The most direct way would be to determine the allele frequencies in a population, wait a few generations, and then determine the frequencies again. If the allele frequencies have changed, then the population has evolved (that's the definition of evolution).

CHAPTER 15 SUMMARY

The theory of evolution—what Darwin called "descent with modification"—draws two main conclusions about life: that all living things are related, sharing a common ancestor in the distant past; and that the species we see today are the result of natural selection operating over millions of years. The theory of evolution is supported by a wealth of evidence, including fossil, anatomical, and DNA evidence. Fossils are the preserved remains or impressions of once-living organisms that provide a record of past life on Earth. Not all organisms are equally likely to form fossils. Fossils can be dated directly or indirectly: on the basis of the age of the rocks they are found in, or on their position relative to rocks or fossils of known ages. When fossils are dated and placed in sequence, they show how life on Earth has changed over time. As predicted by descent with modification, the fossil record shows the same overall pattern for all lines of descent: younger fossils are more similar to modern organisms than are older fossils. Descent with modification also predicts the existence of intermediate organisms, such as Tiktaalik, that possess mixtures of "old" and "new" traits. Tiktaalik has features of both fish and tetrapods (four-limbed vertebrates). An organism's anatomy reflects adaptation to its ecological environment. Changed ecological circumstances provide opportunities for new adaptations to evolve by natural selection. Homology—the anatomical, developmental, or genetic similarities shared among groups of related organisms—is strong evidence that those groups descend from a common ancestor. Homology can be seen in the common bone structure of the forelimbs of tetrapods, the similar embryonic development of all vertebrate animals, and the universal genetic code. Many genes, including those controlling limb development, are shared among distantly related species, an example of molecular homology owing to common ancestry. DNA can be used as a molecular clock: more-closely related species show greater DNA sequence homology than do more-distantly related species

Where did the earliest humans evolve, and how do we know?

There are two main hypotheses concerning human origins. Both place the human birthplace in Africa, but they differ in how recently that birth occurred. According to one hypothesis (the multiregional hypothesis), ancient humans began migrating from Africa about 2 million years ago, journeying subsequently to Europe and Asia. Over the next 2 million years, these groups continued to evolve in these regions, as a single species, eventually becoming modern humans. The second hypothesis (the out-of-Africa hypothesis) is that anatomically modern humans first appeared about 200,000 years ago, in Africa, and spread around the world from there—displacing earlier members of our genus, which became extinct as a result. In 1987, a team of geneticists led by Allan Wilson of the University of California at Berkeley used mitochondrial DNA (mtDNA)—genetic material we inherit solely from our mothers—to construct an evolutionary tree of humanity. Mitochondrial DNA is DNA located in the mitochondria of our cells. Unlike nuclear DNA, which is inherited from both parents and which undergoes recombination during meiosis, mtDNA passes from mothers to offspring essentially unchanged. That's because sperm do not contribute their mitochondria to the newly formed zygote

How Beta-Lactam antibiotics work

anti-biotics are grouped into classes, one of which is called the beta-lactam antibiotics which interfere with a bacterium's ability to synthesize cell walls the absence of antibiotic - the cell wall is a strong, rigid structure -water flowing into the cell exerts pressure on the cell wall - the strong cell wall remains intact in the presence of antibiotics -beta-lactam antibiotics interfere with the proper synthesis of the cell wall. causing it to be weak - water flowing into the cell exerts pressure onto the cell wall -the weakened cell wall breaks apart (cell ruptures)

How Bacterial Populations Acquire Genetic Variation ----reproducing bacterial pop becomes genetically diverse by accumulating ===and by picking genes from other bacteria of the same or diff species (---) Mutations- occur spontaneously during DNA replication every time the bacterial cell replicates. These mutations introduce new ----, and therefore new traits like antibiotic resistance into the population Gene transfer- DNA can pass from one bacterial species to another. A non-staph bacterium, for example, in past teens to S. aureus , Introducing new alleles, and therefore new traits like antibiotic resistance into the population

asexuality mutations gene transfer alleles

almost immediately after antibiotics were introduced, bacteria that could survive antibiotics—drug-resistant bacteria—began to emerge. Within the last decade, drug-resistant bacterial strains have become much more common. Most people infected with drug-resistant bacterial strains are still treatable, but they have fewer treatment options. Drug-resistant strains of staph, for example, are typically resistant to an entire class of antibiotic drugs called ---.---include penicillin and the cephalosporin antibiotics, such as methicillin and cephalexin. Beta-lactams are the most ----prescribed class of antibiotics, used to treat ear infections, bronchitis, and urinary tract infections, among others. They work by interfering with a bacterium's ability to synthesize ---

beta-lactams. Beta-lactams commonly cell walls

Urbanization isn't the only human-caused environmental change that animals face, of course—---is another big one—but it's one that has taken on pressing urgency in recent years. So it's important to understand how our fellow animals are adapting—or not adapting—to city life. If you're an evolutionary biologist and you want to understand how a group of organisms is coping with environmental changes, you need to know something about its underlying ---—and not just the genetics of individuals, but the genetics of the population as a whole. ---allows scientists to understand the nature of evolutionary change as it is reflected in the genes of a population. Essentially, it's a way to take stock of who's reproducing, who isn't, and the consequences for the population as a whole

climate change genetics Population genetics

Inbreeding can have dangerous consequences for a population. Because

closely related individuals are more likely to share the same alleles, the chance of two recessive harmful alleles coming together during mating is high. When that happens, homozygous recessive genotypes are created, and previously hidden recessive alleles start to affect phenotypes in negative ways. This effect is called inbreeding depression.

The theory of evolution—what Darwin called ---draws two main conclusions about life on Earth: that all living things are related, and that the different species we see today have emerged over time as a result of natural selection operating over millions of years. One of the most compelling lines of evidence for evolution comes from ---, the preserved remains or impressions of once-living organisms. Fossils are like snapshots of past life, capturing what life was like at particular moments in time. Fossils are formed in a number of ways: an animal or plant may be frozen in ice, trapped in amber (hardened tree sap), or buried in a thick layer of mud. The entombed organism is thereby protected from being eaten by scavengers or rapidly decomposed by bacteria. Over time, if conditions are right—for example, if the mud encasing the specimen remains undisturbed long enough for hardening to occur—the organism's shape is preserved. Not all organisms are equally likely to form fossils, however: animals with ---are more likely to be preserved than animals without such hard parts (think earthworms or jellyfish) that decay quickly. And conditions permitting fossilization are ---: the organism has to be in just the right place at just the right time

descent with modification— fossils bones or shells rare

Because the very use of antibiotics drives bacterial populations to evolve resistance, antibiotic resistance is inevitable. But humans have hastened the emergence of drug-resistant strains of bacteria by the haphazard use and overuse of antibiotics. Doctors aren't the only culprits Clearly, developing stronger antibiotics isn't the only or the best solution to the problem of resistance because bacteria will ultimately adapt to those, too. Perhaps the best way to control resistance, say experts, is to

from the moment antibiotics were first introduced, physicians began prescribing them for colds, coughs, and earaches, most of which are caused by viruses, rather than bacteria, and so aren't killed by antibiotics anyway. . Approximately 80% of the antibiotics sold in the United States are used for livestock. change practices that enable resistant strains to thrive. It is critical, for example, that when an antibiotic is prescribed it is taken precisely as directed, for the full course of treatment, no matter how much better the patient may be feeling

Fossils Form Only in Certain Circumstances

if the dead organism is preserved quickly by 1- rapid freezing, desiccation, or burial in amber (harden tree sap) = preserved largerly in their OG state 2- rapid burial in sediment layers= quick burial protects body from rapid decay 2- pt2- are the conditions right for fossilization of the buried organism? 2.1 mineralization= hard parts of the body are do not decay rapidly. overtime minerals in water are deposited in spaces within bone as to breaks down. 2.2 imprint or mold= soft mud which a dead organism is burred hardens into rock 2.3 no fossil form= organism gets broken down slowly by bacteria and water

DNA is the molecule of ----, and that it is shared by all living organisms on Earth. Every molecule of DNA—whether from fish, maple tree, bacterium, or human—is made of the same four nucleotides (A, C, T, and G), and all organisms use the information encoded by those nucleotides to make proteins in the same basic way, using the universal genetic code (see Chapter 8). Why should all living things use the same system of decoding genetic information? The best explanation is that this system was the one used by the ancient ancestor of all living organisms, passed on to all of its descendants, and preserved throughout billions of years of evolution. While all living organisms share DNA and the genetic code, no two species share the exact same ====. That's because ---in DNA replication and other ----are continually introducing variation into DNA sequences (and the proteins they encode). Over time, neutral and advantageous mutations will tend to be preserved, while harmful mutations will tend to be selected against and eliminated.

heredity sequence of DNA nucleotides errors mutations

The fact that all tetrapods share the same forelimb bones, arranged in the same order, is an example of --—a similarity due to common ancestry. Darwin provided that explanation: homologous structures are ones that are similar because they are inherited from the ---—in this case, an amphibious creature like Tiktaalik. Why is this significant? Think of it this way: every time you bend your wrist back and forth—to swipe a paint brush or hold a cell phone to your ear, for example—you are using structures that first evolved 375 million years ago in fish. As Shubin points out, "This is not just some archaic, weird branch of evolution; this is our ==="

homology same ancestor branch of evolution

How does the fossil record reveal information about evolutionary changes

if all organisms have descended from a single common ancestor that lived billions of years ago, as the theory of evolution concludes they did, then we would expect the fossil record to show an ordered succession of evolutionary stages as organisms evolved and diversified. And, indeed, that is exactly what we see: prokaryotes appear before eukaryotes, single-celled organisms before multicellular ones, water-dwelling organisms before land-dwelling ones, fish before amphibians, reptiles before birds, and so on. Moreover, we would expect to see changes over time within a family of organisms, and we do

Back then, what is now the Canadian Arctic had a warm, wet climate and a landscape veined by shallow, meandering streams. Early in the Devonian Period there was little plant growth, and the world would have looked fairly brown and empty. By the middle of the Devonian, says Daeschler, if you were standing on the bank of a stream you would have seen some of the first land plants, the first forests, as well as the first ---—spiderlike creatures and millipedes, for example—crawling on land. Still, there would have been no ---vertebrates at this time: nothing with bony limbs, nothing with a backbone or skull. The physical challenges of living on land are very different from those in water. Water provides ===to aquatic animals, supporting their bodies and helping to keep them afloat. By contrast, animals that walk on land have to cope with ----. Air doesn't support land animals, so their bodies need a sturdier structure. Animals on land can also ---out, which is dangerous for them because cells need water to function. And, of course, taking in oxygen is different on land and in water. one of the many features that distinguish land animals from fish, biologists have singled out one as a key evolutionary milesto. Fish do not have limbs, in the sense of jointed, bony appendages with fingers and toes. Instead, they have webbed fins. In most fishes, the fin bones are thin and fan out away from each other. These so-called ray-finned fishes include the modern-day perch, trout, and bass. By contrast, amphibians, birds, most reptiles, and mammals all have two pairs of limbs, defining them as tetrapods (from the Greek for "four-footed"). Tiktaalik is a step closer: "It looks like a fish in that it has scales and fins," Shubin told reporters in 2006 after the discovery, "but when you look inside the skeleton you see how special it really is."

invertebrates land-dwelling buoyancy gravity dry limbs

If they have the same bones, why then do a human arm and a bird wing look so different? Remember that during the process of cell division, mutations are continually being introduced into the DNA of genes, and that when these ---occur in sperm or egg cells, they are inherited. Such mutations can produce subtle changes in the proteins encoded by those genes—proteins involved in constructing the bones that make up an arm or a wing, for example. Changes in bone proteins can result in slightly altered bones, for instance making them longer or thinner. When these modified bones are helpful to an organism's ---, the advantageous traits are passed on to the next generation, and populations emerge that have these adaptations. -------

mutations survival and reproduction This "descent with modification

Staph bacteria became resistant to drugs either by -----or by picking up resistance genes from other drug-resistant bacteria. The genetic changes ultimately altered staph proteins in ways that helped them dodge antibiotic drugs. The altered or acquired genes may code for ----that can disable antibiotics. Or, they may code for proteins with altered shapes to which antibiotics can no longer bind. Some bacteria produce enzymes called beta-lactamases that chew up beta-lactam antibiotics. Because different strains of bacteria have developed antibiotic resistance independently, several genetically unique drug-resistant staph strains circulate through human communities at the same time.

mutations in their own genes proteins

How did these genetic differences among populations come about? One possibility is that each population of mice evolved by ---as a result of local differences in the environment—perhaps each different green space has different predators or food sources, for example—which selected for individuals with different alleles. Given how close these green spaces are to one another, however—in some cases, less than a mile apart—and given also how similar the environments are, this explanation isn't the most likely one. More likely, says Munshi-South, the cause is genetic drift. "Genetic drift is a bit like rolling the --. By simple chance, some individuals survive and reproduce, and others do not." Those that pass on their genes aren't necessarily more fit or better adapted; they're just lucky—perhaps their nest or burrow wasn't swept away in a flash flood, for example. Over time, genetic drift tends to decrease the genetic diversity of a population, as some alleles are lost completely and others sweep to 100% frequency. Genetic drift will have more dramatic effects in ---ones But all populations experience some measure of genetic drift, since chance is a fact of life.

natural selection evolutionary dice smaller populations than in larger

What features make Tiktaalik a transitional fossil, and what role do these types of fossil play in the fossil record? Further excavation revealed the well-preserved remains of several flat-headed animals between 4 and 9 feet long. In some ways, the animals resembled giant fish—they had fins and scales. But they also had traits that resembled those of land-dwelling amphibians—notably, a --- . The researchers named the new species ---; tiktaalik (pronounced tic-TAH-lick) is a native word meaning "large freshwater fish." This ancient hybrid animal no longer exists, but it represents a critical phase in the evolution of four-legged, land-dwelling vertebrates—including humans According to Shubin, a professor of biology at the University of Chicago and the Field Museum of Natural History, Tiktaalik is the most compelling example yet of an animal that lived at the cusp of this important ---. Not only does it fill a gap in our knowledge, the discovery also provides persuasive evidence in support of ---'s theory. For all its amphibian-like adaptations, Tiktaalik is still considered a fish because its limbs lack the true jointed fingers and toes that characterize tetrapod limbs (in other words, they're still fins). But it's by far the most tetrapod-like of all the ancient fishes discovered to date. Scientists have jokingly referred to it as a "fishapod" And that's what makes Tiktaalik such an important find: it occupies a midpoint between fish and tetrapods.

neck, wrists, and fingerlike bones Tiktaalik roseae transition Darwin

However, mutation is a fundamentally random process that does not by itself lead to a population becoming more adapted to its environment. In other words, mutation is a type of ---evolution. The other types of nonadaptive evolution are genetic drift and gene flow. Nonadaptive evolution isn't necessarily "bad," or maladaptive. If mutations didn't introduce variation into a population, there would be no evolution at all. And many nonadaptive changes in allele frequency can be considered "neutral"—neither "good" nor "bad." But nonadaptive evolution can greatly influence the fate of a species, and so researchers are keen to study it.

nonadaptive

Fossils Reveal Changes in Species over Time Descent with modification also predicts that the fossil record should contain evidence of intermediate organisms—those with a mixture of "---" traits. Darwin acknowledged in The ---that the fossil record of his day did not provide many examples of such intermediate organisms—a state of affairs he described as "probably the gravest and most obvious of all the many objections which may be urged against my views." Yet Darwin knew that if his hypothesis were correct, then intermediate fossils would eventually be found. And indeed many have been. Scientists have discovered animals with mixtures of reptile and bird characteristics and animals with mixtures of reptile and mammal characteristics.

old" and "new Origin of Species

Ultimately, the interplay between an organism's traits—its ---—and its environment is what determines what traits will predominate in a population. When the environment favors the survival and reproduction of individuals with certain traits, those traits become more common in the population. The differential survival and reproduction of individuals within a population in response to environmental pressure is called natural selection. when ----acts on a population over time, advantageous traits become more common, and the population becomes better suited to its environment. In other words, evolution by natural selection leads to ---- This is what we see with antibiotic-resistant bacteria: the population has become better suited, or adapted, to an environment in which antibiotics are abundant Note that evolution by natural selection occurs in ----not ---. Individual organisms do not experience a change in allele frequencies over time..

phenotype natural selection adaptation populations, not individuals

From these fossil bones, they determined that Tiktaalik was a ---fish with sharp teeth, scales, and fins. In addition to these fishy attributes, it had a flat skull reminiscent of a crocodile head, as well as a ---. To Shubin and Daeschler, the neck was one of the most surprising finds. Having a flexible neck meant that, unlike a fish, Tiktaalik could swivel its head independently of its body. This feature may have enabled it to catch a glimpse of predators sneaking up on it from behind, or to snap its jaws sideways like a crocodile. Tiktaalik also had the full-fledged ====of a modern land animal, sturdy enough to support the animal's trunk out of water even against the force of gravity. But it is Tiktaalik's ---that have justly made it famous. While possessing many features of a lobe-finned fish, including a sturdy stalk of limblike bones, Tiktaalik appears also to have had a jointed ===bones. Like other fish living at the time, Tiktaalik is thought to have had both ---, which explains how it could breathe out of water for these short excursions. People sometimes assume that lungs were a late evolutionary adaptation, and that they came from modified gills, which modern-day fish use to breathe in water. But in fact, lungs—air-filled organs used for respiration—evolved very early in evolutionary history, more than 375 million years ago. They existed in ---. ---are lobe-finned fish closely related to the lobe-finned fish from which Tiktaalik is believed to have descended. For all its amphibian-like adaptations, Tiktaalik is still considered a fish because its limbs lack the true jointed fingers and toes that characterize tetrapod limbs But it's by far the most tetrapod-like of all the ancient fishes discovered to date. Scientists have jokingly referred to it as a "fishapod"

predatory flexible neck ribs fins elbow, wrist, and fingerlike lungs and gills ancient fish Lungfish

How do genotypes behave in a non-evolving population? A common misconception is that dominant traits will tend to increase automatically in a population and recessives will be eliminated—thus removing variation from the population. Two mathematicians, G. H. Hardy and Wilhelm Weinberg, independently showed in the early 20th century that this was not the case. Through simple mathematical proofs, they showed that genotype frequencies (and therefore allele frequencies) in a population will ----, generation after generation, provided no evolutionary forces—such as genetic drift, natural selection, or gene flow—are bearing down on the population. In other words, in a nonevolving population, the genotype frequencies and allele frequencies will be in ====, and variation will be maintained. Moreover, genotype frequencies in a nonevolving population can be predicted from the ---frequencies. This mathematical observation has come to be known as tprinciple and is a cornerstone of population genetics

remain constant equilibrium allele Hardy-Weinberg

The most common ant species, found on nearly all medians, was an introduced species known as the pavement ant (Tetramorium caespitum), which hails originally from Europe, but ants from as far away as Japan were found Members of different species cannot mate and produce fertile offspring with each other because their populations are ---. Such reproductive isolation can be caused by a number of factors. For example, the two species may have different mating times, locations, or mating rituals—so, like ships passing in the night, they may never meet.

reproductively isolated

many of our most trusted antibiotics are no longer effective at killing the bacteria they once defeated. Over time, these bacteria have changed genetically—evolved—to become As a result, scientists are now seeing bacterial infections that don't respond to any known antibiotics, leading many to fear the day when we run out of treatment options altogether.

resistant

The fossils they found looked like the elusive intermediate creature the team had been hunting for. But how could they be sure it was the right age? Logically, fossils are at least as old as the ---that encase them, so if you know the age of the rocks, then you know the age of the fossils, too. Some types of rocks can be dated directly by ----, in which the proportion of certain radioactive isotopes in rock crystals serves as a geologic clock Fossils found in or near these layers can be dated quite precisely. If fossils are found in rock layers that cannot be directly dated by radiometric dating, they can be dated indirectly by their ----with respect to rocks or fossils of known age that are either deeper or shallower, a technique called ----. Generally speaking, the deeper the fossils, the older they are

rocks radiometric dating position relative dating