Biology Chapter 17 Quiz

Example of Evolution in genetic terms (Figure 17-2 in textbook)

For example, if the frequency of the B allele in Figure 17-2 drops to 30 percent, the population is evolving. it's important to note that populations, not individuals, evolve. Natural selection operates on individual organisms, but the changes it causes in allele frequency show up in the population as a whole.

Sexual Reproduction and Allele Frequency

Gene shuffling during sexual reproduction produces many gene combinations. But a century ago, researchers realized that meiosis and fertilization, by themselves, do not change allele frequencies. So hypothetically, a population of sexually reproducing organisms could remain in genetic equilibrium.

Genetic Recombination in Sexual Reproduction

Mutations are not the only source of heritable variation. Most heritable differences are due not to mutations, but to genetic recombination during sexual reproduction. *Remember* that each chromosome in a pair moves independently during meiosis. In humans, who have 23 pairs of chromosomes, this process can produce 8.4 million gene combinations.

Mutations only matter in evolution when...

Mutations only matter in evolution only if they can be passed from generation to generation. For that to happen, mutations must occur in the germ line cells that produce either eggs or sperm. A mutation in skin cells that produces a nonlethal skin cancer, for example, will not be passed to the next generation.

Natural selection acts differently on ___, not ____.

Natural selection acts differently on phenotype, not genotype. In other words, natural selection acts on the organism's characteristics, not directly on its alleles.

The Founder Effect (Example)

One example of the founder effect is the evolution of several hundred species of fruit flies on different Hawaiian islands. All those species descended from the same mainland fruit fly population. However species on different islands have allele frequencies that are different from those of the original species.

Nonrandom Mating

individuals MUST mate with others at RANDOM. But in many species, individuals select mates based on heritable traits, such as size, strength, or coloration, a practice known as sexual selection. When sexual selection is at work, genes for the traits selected for or against are not in equilibrium.

The more differences there are between the DNA sequences of two species means what?

the more time has elapsed since the two species shared a common ancestor.

Molecular clock (definition)

A molecular clock uses mutation rates in DNA to estimate the time that two species have been evolving independently.

Mutations

A mutation is any change in the genetic material of a cell. Some mutations involve changes within individual genes. Other mutations involve changes in larger pieces of chromosomes.

What produces an organisms phenotype?

An individual's genotype, together with environmental conditions, produces its phenotype.

Timing is Everything

Each part of an embryo starts to grow at a certain time, grows for a specific time, and stops growing at a specific time. Small changes in starting and stopping can make a big difference in organisms. For example, small timing changes can make the difference between long, slender fingers and short, stubby toes.

How is evolution defined in genetic terms?

Evolution, in genetic terms, involves a change in the frequency of alleles in a population over time.

Geographic barriers don't always guarantee isolation?

Floods, for example, may link separate lakes, enabling their fish populations to interbreed. If those populations still interbreed, they remain a single species. Also, a geographic barrier may separate certain organisms but not others. A large river may keep squirrels and other small rodents apart but probably won't isolate bird populations.

Behavioral Isolation (Example)

For example, eastern and western meadowlarks are similar birds whose habitats overlap. But, members of the two species will not mate with each other, partly because they use different songs to attract mates. Eastern meadowlarks don't respond to western meadowlark songs, and vice versa.

2pq =?

Frequency of heterozygous (Aa)

The Founder Effect (Explanation)

Genetic drift may also occur when a few individuals colonize a new habitat. These founding individuals may carry alleles that differ in relative frequencies from those of the main population, just by chance. The new gene pool may therefore start out with allele frequencies different from those of the parent gene pool, as shown in figure 17-8 (490 in textbook). This is known as the founder effect.

Example of Polygenic Trait

Height in humans, height varies from very short to very tall and everywhere inbetween.

Temporal Isolation (Definition)

This happens when two or more species reproduce at different times.

Gene Family Example

Your body, for example, produces a number of molecules that carry oxygen. Several of these compounds - called globins - are hemoglobins. The globin gene family that produces them evolved, after gene duplication, from a single ancestral globin gene. Some of the most important evolution research focuses on another gene family - Hox genes.

A Phenotype includes

all physical, physiological, and behavioral characteristics of an organism, such as eye color or height.

Gene pool

consists of all the genes, including all the different alleles for each gene, that are present in a population.

p=?

frequency of the dominant allele

Allele Frequency

is the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene.

An organism's genotype is what?

is the particular combination of alleles it carries.

Mutations (Genetic Equilibrium)

mutations can introduce new alleles into a gene pool, thereby changing allele frequencies and causing evolution to occur.

What are the two equations of the Hardy-Weinberg principle? (Variables & Numbers)

p^2 + 2pq + q^2 = 1 p+q = 1

Genetic variation and evolution are both studied in

populations

P^2 =?

Frequency of homozygous dominant (AA)

(First Part of Galapagos Hypothesis) Founders Arrive

A few finches from South America, Species M, arrived on one of the Galapagos islands, as shown in Figure 17-13 (496 in textbook). These birds may have gotten lost or been blown off course by a storm. Once on the island, they survived and reproduced. Because of the FOUNDER EFFECT, allele frequencies of this founding finch population could have differed from allele frequencies in the original South American population.

(Fifth and Final Part of Galapagos Hypothesis) Competition and Continued Evolution

As these two new species live together on the first island, they compete for seeds. During the dry season, birds that are most different from eachother have the highest fitness. That is because the more specialized birds have less competition for certain kinds of seeds and other foods. Over time, species evolve in a way that increases the differences between them. The species B birds on the first island may evolve into a new species C. The combined processes of geographic isolation on different islands, genetic change, and behavioral isolation could have repeated itself again and again across the Galapagos chain. Over many generations, the process could have produced the 13 different finch species found there today.

How does natural selection never act differently on genes?

Because it is an entire organism - not a single gene- that either survives and reproduces or dies without reproducing.

How does natural selection affect polygenic traits?

Natural selection on polygenic traits can affect the relative fitness of phenotypes and thereby produce one of three types of selection: directional selection, stabilizing selection, or disruptive selection.

How does natural selection affect single-gene traits?

Natural selection on single-gene traits can lead to changes in allele frequencies and, thus, to change in phenotype frequencies.

How may Hox genes be involved in evolutionary change?

Small changes in Hox gene activity during embryological development can produce large changes in adult animals.

q=?

frequency of the recessive allele

Neutral Mutations as "Ticks"

A molecular clock relies on a repeating process to mark time- mutation. Simple mutations occur all the time, causing slight changes in the sequence of DNA. Some mutations are harmful or beneficial on an organism's phenotype. These types of mutations are under powerful pressure from natural selection. There are many neutral mutations, and these tend to accumulate in the DNA of different species at about the same rate. Researchers can compare such DNA sequences in two species. The comparison can reveal how many mutations have occurred independently in each group. *The more differences there are between the DNA sequences of the two species, the more time has elapsed since the two species shared a common ancestor.*

Small population size

Genetic drift usually does not have major effects in large populations, but can affect small populations strongly. Evolutionary change due to genetic drift thus happens more easily in smaller populations.

Reproductive Isolation (Definition & Example)

Interbreeding links members of a species genetically. Any genetic changes can spread throughout the population over time. But what happens if some members of a population stop breeding with other members? The gene pool can split. Once a population has thus split into two groups, changes in one of those gene pools cannot spread to the other. Because these two populations no longer interbreed.

Polygenic Traits

Many traits are controlled by two or more genes and are called polygenic traits. Each gene of a polygenic trait often has two or more alleles. As a result, a single polygenic trait often has many possible genotypes and even more different phenotypes. Often those phenotypes are not clearly distinct from one another.

Copying Genes

Most organisms carry several copies of various genes. Sometimes organisms carry two copies of the same gene. Other times there may be thousands of copies.

Gene Families

Multiple copies of a duplicated gene can turn into a group of related genes called a gene family. Members of a gene family typically produce similar, yet slightly different proteins.

Calibrating the Clock

Some genes accumulate mutations faster than others, this makes many different clocks, each of which "ticks" at a different rate. In the same way of using the second hand and a minute/hour hand, researchers choose a different molecular clock to compare great apes than to estimate when mammals and fishes shared a common ancestor.

Genetic Bottlenecks

Sometimes, a disaster, such as disease, can kill many individuals in a population. Just by chance, the smaller population's gene pool may have allele frequencies that are different from those of the original gene pool. If the reduced population later grows, its alleles will be different in frequency from the original population's.

Duplicate Genes Evolve

Sometimes, extra copies of a gene undergo mutations that change their function. The original gene is still around, so the new genes can evolve without affecting the original gene function or product. (17-19, 500 in textbook shows this in a diagram)

Disruptive Selection Example

Suppose a bird population lives in an area where medium-size seeds become less common and large and small seeds become more common. Birds with unusually small or large beaks would have higher fitness. As shown in the graph (489 in textbook) , the population might split into two groups: one with smaller beaks and one with larger beaks.

Behavioral Isolation (Definition)

Suppose two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors. Behavioral isolation can then occur.

Geographic Isolation (Example)

The Abert's squirrel in figure 17-2 (495 in textbook), for example, lives in the Southwest. About 10,000 years ago, a small opoulation became isolated on the north rim of the Grand Canyon. Separate gene pools formed. Genetic changes that appeared in one group were not passed to the other. Natural selection and genetic drift worked separately on each group and led to the formation of a distinct subspecies, the Kaibab squirrel. The Abert's and Kaibab squirrels are very similar, indicating that they are closely related. However, the Kaibab squirrel differs from the Abert's squirrel in significant ways, such as fur coloring.

Hardy-Weinberg Equation (Explanation)

The Hardy-Weinberg principle makes predictions like Punnett squares, but for populations, not individuals. Here's how it works. Suppose that there are two alleles for a gene: A (dominant) and a (recessive). A cross of these alleles can produce three possible genotypes: AA, Aa, and aa. The frequencies of genotypes in the population can be predicted by these equations, where p and q are frequencies of the dominant and recessive alleles.

What conditions are required to maintain genetic equilibrium?

The Hardy-Weinberg principle predicts that five conditions can DISTURB genetic equilibrium and cause evolution to occur: (1) nonrandom mating; (2) small population size; and (3) immigration or emigration; (4) mutations; or (5) natural selection.

The Hardy-Weinberg Principle (Definition)

The Hardy-Weinberg principle states that allele frequencies in a population remain constant unless one or more factors cause those frequencies to change.

The bottleneck effect

The bottleneck effect is a change in allele frequency following a dramatic reduction in the size of a population.

(Second Part of Galapagos Hypothesis) Geographic Isolation

The island's environment was different from the South American environment. Some combination of the FOUNDER EFFECT, GEOGRAPHIC ISOLATION, and NATURAL SELECTION enabled the island finch population to evolve into a new species, Species A. Later a few birds from Species A crossed to another island, because these birds do not usually fly over open water, they move from island to island very rarely. Thus, finch populations on the two islands were geographically isolated from each other and no longer shared a common gene pool.

What determines the number of phenotypes for a given trait?

The number of phenotypes produced for a trait depends on how many genes control the trait.

Genotype and Phenotype in Evolution

Typical plants & animals contain two sets of genes, one contributed by each parent. Specific forms of a gene, called alleles, may vary from individual to individual.

A Population is

a group of individuals of the same species that mate and produce offspring. Because members of a population interbreed, they share a common group of genes called a gene pool.

What are the two equations of the Hardy-Weinberg principle? (Words/Description)

(frequency of AA) + (frequency of Aa) + (Frequency of aa) = 100% and (frequency of A) + (frequency of a) = 100%

Single-Gene Traits

A single gene trait is a trait controlled by only one gene. Single-gene traits may have just two or three distinct phenotypes. In populations, phenotypic ratios are determined by the frequency of alleles in the population as well as by whether the alleles are dominant or recessive.

Genetics Joins the Evolutionary Theory

After Mendel's work was rediscovered around 1900's Researchers discovered that heritable traits are controlled by genes that are carried on chromosomes. They learned how changes in genes and chromosomes generate variation. All the discoveries in genetics fit perfectly into the evolutionary theory. Variation is the raw material for natural selection, and finally scientists could study how and why variation occurs. Today, techniques of molecular genetics are used to form and test many hypotheses about heritable variation and natural selection. Modern genetics enables us to understand, better than Darwin ever could, how evolution works.

Directional Selection Example

Consider how limited resources, such as food, can affect individuals' fitness. Among seed-eating birds such as Darwin's finches, birds with bigger, thicker, beaks can feed more easily on larger, harder, thicker-shelled seeds. Suppose the supply of small and medium-size seeds runs low, leaving only larger seeds. Birds with larger beaks would have an easier time feeding than would small-beaked birds. Big-beaked birds would therefore be more successful in surviving and passing on genes to the next generation. Over time, the average beak size of the population would probably increase.

Example of how Hox genes can be involved in evolutionary change

For example, insects and crustaceans are related to ancient common ancestors that possessed dozens of legs. Today's crustaceans, including shrimp and lobsters, still have large numbers of paired legs, but insects have just 3 pairs of legs. What happened to those extra legs?

q^2=?

Frequency of homozygous recessive (aa)

How does natural selection act differently on phenotype?

In any population, some individuals have phenotype that are better suited to their environment than are the phenotypes of individuals. The better-suited individuals produce more offspring than the less fit individuals do. Therefore, organisms with higher offspring than the less fit individuals do. Therefore, organisms with higher fitness pass more copies of their genes to the next generation.

What can mutations do to fitness?

It is possible that mutations that produce changes in phenotype may or may not affect fitness. Some mutations, such as those that cause genetic diseases, may be lethal. Other mutations may lower fitness by decreasing an individual's ability to survive and reproduce. Still other mutations may improve an individual's ability to survive and reproduce.

What are neutral mutations?

Mutations that do not change an organism's phenotype.

How common are mutations?

Recent estimates suggest that each of us is born with roughly 300 mutations that make parts of our DNA different from that of our parents. Most of those mutations are neutral. One or two potentially harmful. A few may be beneficial.

What happened to those extra legs? (Follow-up)

Recent studies have shown that mutations in a single Hox gene, known as Ubx, turns off the growth of legs in the abdominal regions of insects. Thus, a change in one hox gene accounts for a major evolutionary difference between two important animal groups.

Accuracy of Clock

Researchers check the accuracy of molecular clocks by trying to estimate how often mutations occur. In other words, they estimate how many how often the clock they have chosen "ticks". To do this, they compare the number of mutations in a particular gene in species whose age has been determined by other methods.

What are the sources of genetic variation?

Three sources of genetic variation are mutation, genetic recombination during sexual reproduction, and lateral gene transfer.

Species (Definition)

is a population or group of populations whose members can interbreed and produce fertile offspring.

Natural Selection on Single-Gene Traits

*Evolution is any change over time in the allele frequency in a population. This process works somewhat differently for single-gene traits than for polygenic traits. For example, imagine that a population of lizards experiences mutations in one gene that determines body color. The normal color of the lizards is brown. the mutations produce red and black forms. What happens to the new alleles? If red lizards are more visible to predators, they might be less likely to survive and reproduce. Therefore, the allele for red coloring might not become common. Black lizards, on the other hand, might absorb more sunlight and warm up faster on cold days. If high body temperature allows the lizards to move faster to feed and avoid predators, they might produce more offspring than brown forms produce. The allele for black color might increase in frequency. The black phenotype would then increase in frequency. If color change has no effect on fitness, the allele that produces it will not be under pressure from natural selection.

What is a current hypothesis about Galapagos finch speciation?

According to this hypothesis, speciation in Galapagos finches occurred by founding of a new population, geographic isolation changes in the new population's gene pool, behavioral isolation, and ecological competition.

Crossing-Over

Crossing-over is another way in which genes are recombined. Crossing-over occurs during meiosis. In this process, paired chromosomes often swamp lengths of DNA at random. Crossing-over further increases the number of new genotypes created in each generation, this is why no two siblings look exactly the same (except identical twins), With independent assortment and crossing-over, you can easily end up mother's eyes, your father's nose, etc...

Temporal Isolation (Example)

For example, suppose three similar species of orchids live in the same rain forest. Each species has flowers that last only one day and must be pollinated on that day to produce seeds. Because the species bloom on different days, they cannot pollinate one another.

Stabilizing Selection Example

For example, the mass of human infants at birth is under the influence of stabilizing selection. Very small babies are likely to be less healthy and, thus, less likely to survive. Babies who are much larger than average are likely to have difficulty being born. The fitness of these smaller or larger babies is, therefore, lower than that of more average-size individuals.

Genetic Equilibrium (Definition)

If a population is not evolving, allele frequencies in its gene pool do not change, which means that the population is in genetic equilibrium.

Natural Selection

If different genotypes have different fitness, genetic equilibrium will be disrupted, and evolution will occur.

(Fourth Part of Galapagos Hypothesis) Behavioral Isolation

Imagine that a few birds from the second island cross back to the first island. With population A birds breed with population B birds? Probably not. These finches choose mates very carefully. During courtship, they closely inspect a potential partner's beak. Finches prefer to mate with birds that have the same-size beak as they do. Big-beaked birds prefer to mate with other smaller-beaked birds. Because the populations on the two islands have evolved differently sized beaks, they would probably not mate with each other. Thus, differences in beak size, combined with mating behavior, could lead to REPRODUCTIVE ISOLATION. The gene pools of the two bird populations will remain isolated, even when individuals live in the same place. The populations have now become two distinct species.

Lateral Gene Transfer

In most eukaryotic organisms, genes are passed only from parents to offspring (during sexual or asexual reproduction). Some organisms, however, pass genes from one individual to another. *Bacteria swap genes on plasmids as though genes were trading cards. The passing of genes from one organism to another organism that is not its offspring is called lateral gene transfer. Lateral gene transfer has been common, and important, in single-celled organisms during the history of life.

What is genetic drift?

In small populations, an allele can become more or less common simply by chance. In small populations, individuals that carry a particular allele may leave more descendants than other individuals leave, just by chance. Over time, a series of chance occurrences can cause an allele to become more or less common in a population. This kind of random change in allele frequency is called genetic drift.

Immigration or Emigration

Individuals who join a population may introduce new alleles into the gene pool, and individuals who leave may remove alleles. Thus, any movement of individuals into (immigration) or out of (emigration) a population can disrupt genetic equilibrium, a process known as gene flow.

Example of Allele Frequency (Figure 17-2 in textbook)

Mouse population, the allele frequency of the dominant B allele is 40 percent, and the allele frequency of the recessive b allele is 60 percent. The allele frequency of an allele has nothing to do with whether the allele is dominant or recessive. In this mouse population, the recessive allele occurs more frequently than the dominant allele.

Where do new genes come from?

One way in which new genes evolve is through the duplication, and then modification, of existing genes.

(Third Part of Galapagos Hypothesis) Changes in Gene Pools

Over time, populations on each island adapted to their local environment. Plants on the first island may have produced small, thin-shelled seeds, whereas plants on the second island may have produced larger, thick - shelled seeds. On the second island, DIRECTIONAL SELECTION would have favored individuals with larger, heavier beaks. These birds could crack open and eat the large seeds more easily. Thus, birds with large beaks would be better able to survive on the second island. Over time, natural selection would have caused that population to evolve larger beaks, forming a distinct population, B, characterized by a new phenotype.

Where do those extra copies come from, and what happens to them?

Remember that homologous chromosomes exchange DNA during meiosis in a process called crossing-over. Sometimes crossing-over involves an unequal swapping of DNA. That extra DNA can carry part of a gene, a full gene, or a longer length of chromosome. Sometimes, in different ways, an entire genome can be duplicated.

Speciation (Definition)

The formation of new species.

The Founder Effect (Definition)

The founder affect is a situation in which allele frequencies change as a result of the migration of a small subgroup of a population.

Directional Selection

When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end, directional selection occurs. The range of phenotypes shifts because some individuals are more successful at surviving and reproducing than are others.

Disruptive Selection

When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve, disruptive selection occurs. Disruptive selection acts against individuals of an intermediate type. If the pressure of natural selection is strong and lasts long enough, this situation can cause the single curve to split into two. In other words, disruptive election creates two distinct phenotypes.

Stabilizing Selection

When individuals near the center of the curve have higher fitness than individuals at either end, stabilizing selection takes place.

What types of isolation lead to the formation of new species?

When populations become reproductively isolated, they can evolve into two separate species. Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographical isolation, and temporal isolation.

Geographic Isolation (Definition)

When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water, geographic isolation occurs.