Ch13 How Populations Evolve

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3 These crossover events increase the genetic variation among gametes.

1. Environmental Change examples

Camouflage: a drought causes a habitat to turn dry and brown. Pesticides: Pesticide is applied to a population of insects.

Remember that color is an inherited trait in beetles. Which of the following is an example of natural selection?

Green beetles leave more offspring than brown beetles because they are better at finding food. Natural selection occurs when organisms with one inherited trait survive and reproduce more than organisms with other traits.

Natural selection is best described as _____.

a filtering process that fine-tunes the traits of populations by sorting among existing, randomly produced variations

In natural selection, _____ determine which phenotypes are successful.

current conditions in the local environment - natural selection occurs through an interaction between the environment and the variability inherent among individual organisms making up a population.

The _____ of life arises from the adaptation of species to different habitats over long spans of time

diversity

The wing of a bat is homologous to the _____ of a whale.

flipper - bones of a bat wing and a whale flipper are homologous

Consider a population of birds living on an island. Suppose several individuals of the same species from a different population migrate to the island. Due to the arrival of the new birds, the allele frequencies in the original population change. What mechanism of microevolution is at work in this example?

gene flow This is an example of gene flow because new individuals have joined the population, bringing their own alleles with them and thus changing the allele frequencies of the original population.

All the genes in a population are that population's _____.

gene pool All the alleles of all the genes of a population make up a gene pool.

Evolution that occurs by _____ results in a change in a population's gene pool due to chance.

genetic drift

Modern travel along + migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift Modern travel and migration decreases the chances of there being a small, isolated population.

causes of evolutionary change

genetic drift gene flow mutation natural selection

The evolution of populations due to chance is

genetic drift. Genetic drift describes the evolution of a population due to chance.

The original source of all genetic variation is __________.

mutation Mutation is, in itself, very important to evolution because it is the original source of the genetic variation that serves as the raw material for evolution.

Darwin proposed a mechanism for how evolution occurs, which he called _____

natural selection

Evolution that occurs by _____ results in nonrandom reproductive success and adaptive change.

natural selection

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes This process produces chromosomes containing genes inherited from both parents.

Darwin inferred that those organisms w/ traits best suited to the environment tend to leave more _____ than other members of a population.

offspring

Charles Darwin

proposed natural selection as the mechanism of evolution - Darwin, as well as Wallace, proposed natural selection as the mechanism of evolution.

Genetic variation in a population of animals or plants depends mainly on?

sexual reproduction Fresh assortments of existing alleles arise every generation from 3 random components of sexual reproduction: crossing over, independent orientation of homologous chromosomes at metaphase I of meiosis, and fertilization of different gametes.

Organisms that possess homologous structures probably __________.

share a common ancestor that also had this structure - homology refers to similarity attributable to common ancestry. Homologous structures, both anatomical and molecular, can be used to determine the branching sequence of an evolutionary tree. Some homologous characters (genetic code) are shared by all species because they date to the deep ancestral past. In contrast, characters that evolved more recently are shared only w/in smaller groups of organisms.

Which of the following structures would be the LEAST likely to fossilize?

skin - soft tissues such as skin are much less likely to fossilize than harder structures such as bones / shells

All of life is related through common ancestry, accounting for the _____ of life.

unity

Compare sickle cell disease and malaria.

Sickle cell disease and malaria are both potentially lethal diseases. Though malaria is an infectious disease and sickle cell disease is inherited, both can cause life-threatening conditions.

The top figure shows beak sizes of the 1976 finch population before the drought of 1977 (red bars) and after the drought (black bars). The lower figure shows the beak sizes of the offspring of the drought survivors in 1978. What do these figures tell us?

The overall beak depths of the 1978 offspring population are larger the original 1976 population. As mentioned in the film, the average beak depth of the population increased by more than 4% in just one generation.

If a person has 2 normal copies of the hemoglobin allele, which statements are true?

The person is homozygous at the hemoglobin locus. The person is susceptible to malaria. A person with two copies of any allele is homozygous. A person with two normal copies of the hemoglobin allele is more susceptible to malaria than someone with a sickle cell hemoglobin allele.

How did the Grants test their hypothesis that differences in birds' songs can keep different species of finches from breeding w/ one another?

They played the songs of medium ground finches and cactus finches through a loudspeaker to see which species responded to each song. The Grants' experiments using recorded finch songs showed that finch species respond to their own song and not to the song of other species. This is an example of reproductive isolation, which keeps species apart.

Imagine that 4 people are infected w/ HIV from a common source (an infected blood sample). Initially, the patients' HIV populations are genetically identical. By the time they develop full-blown AIDS, how would the viral populations of the 4 patients compare?

Each patient's viral population would be unique, specifically adapted to deal with—and overcome—his or her unique immune system responses.

What contributes the most to genetic variation among individuals in most prokaryote species?

mutation In prokaryotes, which are haploid with a single allele for each gene, mutations immediately have their full effect. Since their generation times are very short, new mutations can proliferate rapidly.

The ease w/ which humans travel across the globe is likely to increase _____.

gene flow When people travel / migrate, they take their alleles w/ them.

Evolution that occurs by _____ results in a change in a population's gene pool due to the movement of individuals into and out of the population.

gene flow

In a population with brown and green alleles for color, genetic drift

has more effect on the evolution of a small population. Genetic drift affects the evolution of small populations more than it affects the evolution of large populations.

Generation-to-generation change in the allele frequencies in a population is _____.

microevolution Generation-to-generation change in the allele frequencies in a population is the definition of microevolution.

The phrase Darwin used to describe his broad theory of evolution is ''descent with _____"

modification

3. Change in Population examples

Camouflage: Brown Beetles survive to reproduce more than Green Beetles do. The Brown Allele increases in frequency. Pesticides: The surviving insects reproduce. The frequency of resistant insects in the population increases.

2. Selective Pressure examples

Camouflage: Green Beetles are more visible to Birds than Brown Beetles, so Birds eat more Green Beetles Pesticides: Some insects have a gene that makes them resistant to the pesticide. These insects survive. Insects w/out the gene die.

Observation of Natural Selection in action - Scientific Evidence:

- development of pesticide resistance in insects - changes in average beak size in finches following dry or wet years

Fossil Record - Scientific Evidence:

- discovery of bones from many different dinosaur species - transitional forms that link whales w/ land-dwelling ancestors that are now extinct

Anatomical & Molecular Homologies - Scientific Evidence:

- similar forelimb anatomy in different species of mammals - same genetic language of DNA and similar genes in yeasts, fruit flies, and humans

Biogeography - Scientific Evidence:

- unique collection of marsupial mammals in Australia - resemblance of island species to nearby mainland species

which represents the occurrence of evolution at its smallest scale?

A pesticide spray is heavily used on a particular farm. Initially it kills 98% of the grasshoppers on contact. Over several generations, the local grasshopper population becomes resistant to the pesticide through inheritance of resistance alleles. Other nearby grasshopper populations do not change in any noticeable way. There has been evolutionary (generation-to-generation, genetically based) change within a single population, the smallest scale of evolution.

Which is a homozygous genotype?

AA When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene.

Suppose that every few years, all people over 6 feet tall do not have any children. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency. A reduction in "tallness" alleles is the change expected as a result of this type of selection.

Which time point on the graph shows when the antibiotic was first added?

B The addition of an antibiotic would kill most of the bacteria in a population, causing the population size to decline rapidly. This is the case at time point B.

The Grants witnessed strong selection during droughts in 1977 and 1985. Compare the 2 droughts.

Both droughts events provided strong natural selection on medium ground finch populations. Both droughts resulted in changes to food sources that favored the survival of some medium ground finches over others. Natural selection simply favors the characteristics that are best in a particular situation. If the situation changes, natural selection favors different characteristics. The primary food source after the 1977 drought was large, hard seeds, which favored large-beaked birds. The primary food source after the 1985 drought was small seeds, which favored small-beaked birds.

In 1977, medium ground finches on Daphne Major experienced a severe drought. The figure shows the beak depths of the initial population before the drought (red bars) and of the drought survivors (black bars). What do the data show?

Finches w/ larger beaks had a survival advantage in the 1977 drought. More than one-half of the initial population died during the drought. The most common beak size of the initial population was 8.8 millimeters. A very small proportion (~5%) of the initial population with this beak size survived. Most of the survivors of the 1977 drought had larger beaks. When small seeds became scarce in the drought, more medium ground finches with smaller beaks ran out of food and died. Finches w/ larger beaks were better able eat the larger, harder seeds.

Which mechanism? New individuals move into a population.

Gene flow

Color is an inherited trait in beetles. If brown beetles move into a population from a nearby island, which of the following statements is correct?

Gene flow causes the frequency of the brown allele to increase. Gene flow occurs when individuals move into or out of a population, changing the allele frequencies in the population. In this case, new brown beetles in the population cause the frequency of the brown allele to increase.

Which mechanism? By chance, some wildflowers in this population reproduce, while others do not.

Genetic Drift

Consider a population of snowshoe hares in Montana. Their fur color changes in response to changes in day length. During the long summer days, they have brown fur, but as the days shorten in the fall, their fur turns white in preparation for winter. Then as the days get longer in the spring, their fur turns brown again. Their fur coloration acts as camouflage from predators. As climate change brings warmer fall temperatures to Montana, colder temperatures with snowfall are coming later in the year, and there may be less snowfall overall. As a result, the hares' fur color may be mismatched to the color of their surroundings, making them more visible to predators. Which snowshoe hares would have a reproductive advantage in this changing environment?

Hares w/ a mutation that causes them to change color in response to temperature rather than day length Snowshoe hares whose fur coloration patterns most closely match their surroundings will be more likely to survive and thus have a reproductive advantage. In this case, if showshoe hares changed fur color in response to temperature rather than day length, they might more closely match their environment. Natural selection would favor those hares in this changing environment.

How did Dr. Allison test his hypothesis that sickle cell disease was connected to malaria?

He evaluated blood samples for malaria parasites and the presence of sickle cells. He expanded his study area beyond Kenya to the rest of East Africa to see if malaria and sickle disease were connected. Dr. Allison gathered blood samples from more than 5,000 children in East Africa. He analyzed the samples to identify malaria parasites and sickle cells. He found that children carrying the sickle cell character (or trait) had a lower parasite count, as if they were partially protected against malaria.

In 1949, Dr. Tony Allison observed a high frequency of Kenyans carrying the sickle cell allele in coastal areas and near Lake Victoria, but a lower frequency in the highlands. What did he hypothesize?

He hypothesized that there was a connection between malaria and sickle cell disease. On the basis of this hypothesis, Dr. Allison predicted high frequencies of sickle cell disease only in areas where malaria is common.

As proposed by Darwin, what sorts of traits are favored by natural selection?

Heritable traits that help individuals survive and reproduce more successfully than others in the same population.

How does Dr. Allison's work provide an example of natural selection in humans?

In areas without malaria, individuals w/ 2 sickle cell alleles reproduced at lower rates than those w/out sickle cell disease. In areas with malaria, individuals w/ 1 sickle cell allele reproduced at higher rates than those w/ no sickle cell alleles. In different environments, natural selection favors different characteristics. In areas with malaria, the reproductive advantages of having one sickle cell allele (and some protection from malaria) kept the allele at high frequencies in the population. In areas without malaria, the reproductive disadvantages from sickle cell disease reduced the allele in populations.

Which example below presents a misconception about how antibiotic resistance develops?

Individual bacteria and viruses become immune to antibiotics after they are exposed to them. Eventually the antibiotics are useless. Antibiotics have no effect on viruses, so this is one common misconception. More importantly, antibiotic resistance arises over several bacterial generations as resistant bacteria flourish and vulnerable strains die out. Although they are usually rare, the resistance traits are often present before the antibiotic is first used.

In some populations, 1 in 500 people have sickle cell disease. What reason does the film give for why a potentially deadly, inherited disease is found at such high frequencies?

Individuals with one sickle cell allele are protected from malaria and do not have sickle cell disease, thus keeping the allele in the population. People w/ 1 sickle cell allele are protected from malaria, but do not have sickle cell disease. Protection from malaria comes at the cost of more sickle cell disease in the population

The film defines species as populations whose members don't interbreed. What keeps different Galápagos finch species from mating?

Males only court females that have a similar beak and similar size. Geographic isolation and different environments led to changes in traits that affected mating. Individuals recognize and only respond to songs of their own species. The Grants and their team gathered evidence to show that finches choose mates on the basis of song and appearance. Changes in behavior can help create reproductive isolation, which keeps species from mating.

Genetic evidence supports which of the following explanations for the presence of 13 different finch species on the Galápagos islands?

Many years ago, a small population of a single finch species migrated to the islands and evolved into the current 13 species. The Galápagos finch DNA reveals that the finch species are more related to each other than to any species on the mainland.

Which mechanism? A prominent tail helps the peacock attract a mate.

Natural Selection

Which mechanism? Camouflage enables this insect to evade predators.

Natural Selection

Natural selection and evolution are 2 terms that are sometimes confused, even by first year biology students. What is the relation between natural selection and evolution?

Natural selection is 1 of several mechanisms of evolution. Modern species evolved from ancestral forms, and natural selection is the main mechanism for adaptation, but other forms of microevolution also contribute to evolutionary change.

The human immune system cannot effectively suppress the HIV virus on its own. What key feature of HIV makes it so hard to beat?

The HIV virus has an extremely high rate of mutation.

Which are homologous to the bones of a whale?

The digits of a cat are homologous to those of these whale bones

Which statements may correctly explain why the population size increases after time point C?

The few drug-resistant bacteria in the population reproduced, quickly leading to a large drug- resistant population. Between time points C and D, drug-resistant bacteria were reproducing faster than non-drug resistant bacteria were dying. Bacteria that acquired a mutation that conferred drug- resistance had a growth advantage over non-resistant bacteria.

Which best describes the fossil record?

The fossil record is the highly ordered sequence in which fossils are found in layers of sedimentary rock - the order is most apparent when we look at the "big picture" of the appearance of life-forms over long periods of Earth's history

A population of small fish lives in a lake with a sandy bottom. The major predator of these fish is a wading bird that hunts by sight. Most of the fish are light sandy brown, but about 10% are mottled. The color pattern is heritable. A construction company dumps a load of gravel in the bottom of the lake, giving it a mottled appearance. Which of these statements presents the most accurate prediction?

The proportion of mottled fish will increase over time. The mottled fish will tend to escape predation because they are camouflaged against the mottled lake bottom, and so the mottled fish will be able to leave more offspring.

Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated.

The sickle cell allele will decrease in frequency. - Without malaria, selection for the sickle cell allele decreases. As a result, the frequency will likely decrease.

Sickle-cell disease is a debilitating disease that results from being homozygous recessive for the "sickle-cell allele" of a hemoglobin gene. Why is the allele present and even common in many human populations?

The sickle-cell allele confers malaria resistance to heterozygotes. In some regions where malaria is common, heterozygotes have an advantage over both homozygotes, and their reproductive success maintains the recessive allele at a high frequency in the population. This illustrates the concept of "heterozygote advantage" as a form of balancing selection.

This unequal reproduction in a population leads to the gradual accumulation of _____ to the environment.

adaptions

HIV has become an important source of mortality for humans. If AIDS persists as a major factor for humans for many generations in the future, natural selection theory predicts that _____.

any heritable traits that help humans survive and reproduce in the presence of AIDS should become more frequent over time

2 key observations underlying natural selection are that members of a population vary in their _____ and that all species can produce more offspring than the environment can support.

inherited traits

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase I This describes metaphase I.

A change in allele frequencies in a population over a span of generations is _____

microevolution

If color is an inherited trait in Beetles, and Birds are more likely to eat Brown Beetles than green beetles,

the frequency of the Green Allele will increase. If Birds are more likely to eat Brown Beetles than Green Beetles, then Green Beetles will survive and reproduce more than Brown Beetles. This causes the frequency of the Green Allele to increase.

Genetic drift is a process based on _____.

the role of chance Genetic drift requires a small sample size

A mutation occurs when _____.

there is a change in the DNA sequence of a gene This is the definition of mutation.

The first tetrapods (4-legged animals) were amphibians, which evolved from a specialized group of lobed-fin fish. An unusual fossilized animal ( Tiktaalik) was recently found; possessed a mixture of fish + amphibian characteristics. What is the term used to describe such an intermediate organism?

transitional form - transitional forms represent a link between ancestral and descendant groups; they possess features of both groups

Which of these gametes contain 1 or >1 recombinant chromosomes?

B, C, F, G These gametes carry chromosomes produced as a result of crossing over.

Different finch species have beaks of different shapes and sizes. What do these beak differences tell us?

Different finch beak shapes are evidence that finch species adapted to different environments over many generations. Having the correct beak shape for a particular food source is important for survival. As Rosemary Grant says, "Beaks are tools, you need the right tool for the right job."

Why is natural selection considered to be the most important mechanism of microevolution?

Natural selection is the only mechanism that consistently leads to adaptive changes in populations. Because natural selection consistently leads to nonrandom adaptive changes in a population, it is considered the most important mechanism of microevolution.

Which of the following is a misconception regarding natural selection?

Natural selection progressively refines organisms' adaptations, eventually leading to perfection. This is a misconception. Natural selection is not "progressive" toward a fixed goal. Instead, it tracks a changing environment. In addition, natural selection cannot produce perfection, partly because adaptations often involve compromises.