Evolution Exam 2

determining the extent to which genotype influences variation in phenotype.

"Common garden" experiments, which expose different genotypes to a common environment, are useful for determining how mutations affect fitness. determining the extent to which genotype influences variation in phenotype. estimating how much a trait will change after positive selection. Testing for genetic correlations among traits.

Directional selection increasing bill size towards a new optimum

Imagine a population of Galápagos finches that vary for bill size. If the population mean is near the optimum size for eating the seeds found on the island, what would we expect to occur if their main seed resource goes extinct, and another plant with much larger seeds replaces it? Directional selection increasing bill size towards a new optimum Stabilizing selection maintaining the population average Disruptive selection increasing phenotypic variance for bill size Extinction of the new plant as finches each all its seeds Correlational selection between seed size and bill size

maintains genetic variation within subpopulations

Migration-selection balance... leads to loss of local allels in the population being invaded prevents local adaptation results in gene swamping maintains genetic variation within subpopulations

can result in an allele with a low relative fitness to persist in populations despite being selected against

Migration-selection balance... will result in the decrease of genetic variance in a population prevents polymorphisms from persisting in a population can result in an allele with a low relative fitness to persist in populations despite being selected against allows for local adaptation in the population being invaded

Genetic drift is nonadaptive; it changes allele frequency without regard to fitness.

Natural selection and genetic drift are the two most important causes of evolutionary change. How do they differ? Only genetic drift has been observed in populations of finite size. Only natural selection can change the frequencies of alleles in a population. Natural selection focuses on the survival of individuals, while genetic drift refers to which individuals actually reproduce. Genetic drift is nonadaptive; it changes allele frequency without regard to fitness. Natural selection involves a population moving toward a goal, while genetic drift is not directed.

Directional selection to a softer fruit than modern animals can eat and disperse its seeds.

Osage orange is a tree that evolved when giant ground sloths were alive and relied on the sloths to eat the softball-sized fruits that were incredibly hard to disperse the seeds through their feces. Osage orange still exists today. Since the ground sloths went extinct, no other animals exist that can crack open the very hard fruits. What type of selection should osage orange populations have experienced for fruit hardness? frequency-dependent selection to maintain variation in fruit hardness in case a new animal evolves to eat hard fruits. Directional selection to a softer fruit than modern animals can eat and disperse its seeds. Stabilizing selection maintaining the population average fruit hardness Disruptive selection for softer and harder fruit.

changes in allele frequencies in a population in the absence of selection.

Genetic drift results in changes in allele frequencies in a population in the absence of selection. the maintenance of heterozygosity in the population. non-random selection on alleles that confer fitness benefits. a dramatic reduction in population size.

a decrease in the likelihood that those alleles will be inherted together

Genetic recombination of alleles at different loci results in those alleles being more likely to be inherited together than if there was no recombination a decrease in the likelihood that those alleles will be inherted together an increase in linkage disequilibrium a decrease in linkage equilibrium

linkage equilibrium

Genetic recombination of alleles at different loci results in those alleles being more likely to be inherited together than if there was no recombination decreased heterozygosity linkage disequilibrium linkage equilibrium

the size of the population

The rate of evolution of an allele under positive selection is a function of all of the following EXCEPT the strength of selection the amount of genetic variation in the population the mode of inheritance of the alleles the size of the population

environmental variance and additive genetic variance

There are several sources of phenotypic variance of quantitative traits. Which two contribute the most variance pleiotropy and linkage disequilibrium dominance variance and environmental variance epistasis and linkage disequilibrium non-additive genetic variance environmental variance and additive genetic variance

Genes that control head plumage phenotypes are under strong selection.

This figure shows how head plumage phenotypes (yellow, left line) and a random set of ancestry genes (green, right line) of wagtail bird species change over a transect of 3000 km. alba species are found from 0 to 1000 km and personata species are found from 1000 to 3000 km. Which statement below is correct? Genes that control head plumage phenotypes are under strong selection. Alba ancestry genes are not flowing into the personata gene pool. If we sampled birds at 1500km we would find that most birds have an alba-like head phenotype There is no gene flow between alba and personata

additive genetic variance environmental variance dominance variance epistatic variance

Total phenotypic variance of a quantitative trait is comprised of which of the following? -environmental variance -additive genetic variance -additive genetic variance and non-additive variance -additive genetic variance environmental variance dominance variance epistatic variance

the amount of gene flow and the strength of selection

Tracking the frequency of an allele under selection over geographic distance shows clines of various widths. The width of a cline depends on ____ and ___

either lost or fixed.

Two alleles segregate at a locus. Assuming that no stabilizing forces exist, the first allele will eventually be either lost or fixed. lost. fixed.

h2 heritability is a characteristic of a population in a given environment.

Given the relationship between h2 and total phenotypic variance (P) where P = additive genetic variance + environmental variance + dominance variance + epistatic variance. What can be concluded about the h2 heritability measure? h2 can not be estimated unless the identity of the genes involved in the phenotype are known. h2 heritability of a trait measured in one population will also be the h2 of the trait in another population of the same species. h2 heritability is a characteristic of a population in a given environment. h2 is dependent only on genetic factors so environment has no influence on its value.

h2 heritability of a trait a function of the environment the genotype is experiencing, so h2 values for the same trait can be very different across populations.

Given the relationship between h2 and total phenotypic variance (P) where P = additive genetic variance + environmental variance + dominance variance + epistatic variance. What can be concluded about the h2 heritability measure? h2 heritability of a trait measured in one population will also be the h2 of the trait in another population of the same species. h2 can not be estimated unless the identity of the genes involved in the phenotype are known. h2 heritability of a trait a function of the environment the genotype is experiencing, so h2 values for the same trait can be very different across populations. h2 is dependent only on genetic factors so environment has no influence on its value.

directional selection

If a population initially shows a symmetric phenotypic distribution (left graph), then shows a left skewed distribution after selection (right graph) what is the most-likely cause? negative-frequency dependent selection stabilizing selection disruptive selection directional selection

quantitative trait

If a trait is encoded by many loci in the organisms genome and the population shows continuous variation in the trait, we refer to it as a single nucleotide polymorphism a discrete trait mendelian trait quantitative trait

Despite the fitness advantage, Fi will barely increase in frequency for many generations, then suddenly rapidly increase.

A population of flowering plant that is fixed for the Fa allele at a locus that encodes a key enzyme in the pathway that enables desiccation tolerance (resists water loss). A drought event rapidly changes the soil conditions over 100 generations. The Fa allele is an adaptation to wetter soils. A new mutation Fi appears and produces an enzyme that can operate better in drier soil. If the relative fitness is as follows, what is predicted to happen? FaFa w = 0.25 FaFi w = 0.25 FiFi w = 1 Fa starts at a higher frequency and because FaFa and FaFi have the same fitness, Fa will never change in frequency. Fi has higher fitness than Fa and will rapidly increase in frequency by positive selection. The population will reach a polymorphic equilibrium because there are two alleles instead of Fa being fixed. Despite the fitness advantage, Fi will barely increase in frequency for many generations, then suddenly rapidly increase.

The population will reach a polymorphic equilibrium because ZaZi shows overdominance.

A population that is fixed for the Za allele at a locus that encodes a key enzyme in the pathway that enables cellular respiration. A glaciation event rapidly changes the climate over 1000 generations. The Za allele is an adaptation to warmer climates. A new mutation Zi appears and produces an enzyme that can operate better in cold temperatures. If the relative fitness is as follows, what is predicted to happen? ZaZa w = 0 ZaZi w = 1 ZiZi w = .75 The population will reach a polymorphic equilibrium because ZaZi shows overdominance. The population will reach a polymorphic equilibrium because ZaZi shows underdominance. Zi has higher fitness than Za and will rapidly go to fixation by positive selection Za has lower fitness than Zi and will rapidly go to loss by purifying selection

Za will be fixed if the initial frequency is above some threshold because ZaZi shows underdominance

A population that is polymorphic for the Za and Zi allele at a locus that encodes a key enzyme in the pathway that enables cellular respiration. A glaciation event rapidly changes the climate over 1000 generations. The Za allele is an adaptation to warmer climates, Zi encodes an enzyme that can operate better in cold temperatures. If the relative fitness is as follows, what is predicted to happen? ZaZa w = 0.25 ZaZi w = 0 ZiZi w = 1 Za will be fixed if the initial frequency is above some threshold because ZaZi shows underdominance. Za will be lost because it has lower fitness than Zi The population will reach a polymorphic equilibrium because ZaZi shows underdominance. Zi is adapted to colder weather so it will go to fixation

A population that is polymorphic for the Za Za will be fixed if the initial frequency is above some threshold because ZaZi shows underdominance.

A population that is polymorphic for the Za and Zi allele at a locus that encodes a key enzyme in the pathway that enables cellular respiration. A glaciation event rapidly changes the climate over 1000 generations. The Za allele is an adaptation to warmer climates, Zi encodes an enzyme that can operate better in cold temperatures. If the relative fitness is as follows, what is predicted to happen? ZaZa w = 0.25 ZaZi w = 0 ZiZi w = 1 Za will be lost because it has lower fitness than Zi Zi is adapted to colder weather so it will go to fixation The population will reach a polymorphic equilibrium because ZaZi shows underdominance. Za will be fixed if the initial frequency is above some threshold because ZaZi shows underdominance.

drift

A previously large population of Threadfin shad (fish) that breed in the brackish water portion on the James River in Virginia experienced a population bottleneck after a harmful algal bloom killed lots of fish. Consider a locus in the genome that has two alleles present in the population (either A1 or A2) but the gene has no impact on fitness. DNA repair is efficient at preventing mutations from occurring, there is no gene flow, and fish mate randomly. Which evolutionary force is most likely to act on this locus over subsequent generations? none natural selection drift sexual selection

Each population will eventually go to fixation for some neutral loci, but the alleles that are fixed will be random across populations.

A previously large population of gopher tortoises distributed across a continuous geographic range becomes fragmented by agricultural development. Now tortoises populations contain relatively few individuals and are isolated as "islands" amidst an "ocean" of crop fields. The island environment has not changed, it is only smaller and discontinuous compared to the original environment. What is likely to happen to neutral loci at each of these isolated populations of tortoises over many generations? The allele frequencies at these loci will remain unchanged from the large population because the environment is the same Each population will eventually go to fixation for the same alleles at all neutral loci. The amount of heterozygosity will increase across all populations, but how large of an increase will be random. Each population will eventually go to fixation for some neutral loci, but the alleles that are fixed will be random across populations.

overdominance

All of the following modes of selection eventually eliminate genetic variation at a locus under selection EXCEPT Overdominance Positive Selection Underdominance Positive-frequency dependent

there is strong linkage disequilibrium betwen this allele and the allele that is under positive selection

An allele that is not directly under positive selection can increase in frequency in the population over generations if there is strong linkage disequilibrium betwen this allele and the allele that is under positive selection recombination is high enough to break up linked alleles that allele is fixed in the population only if that allele has also recently been positively selected

effective population size, strength of genetic drift

As _____ decreases, the ______ increases total population size, strength of genetic drift strength of genetic drift, probability of allele fixation effective population size, strength of genetic drift effective population size, probability of positive selection

Genetic variation will decline as alleles randomly go extinct.

Consider a hypothetical locus with several alleles in a population that is small. Mutation is absent, and none of the alleles has a selective advantage. Which of the following is likely to occur after a long period of time (many generations)? Allele frequencies will change over time, but all alleles will remain. Allele frequencies will cycle over time. Balancing selection will maintain all the alleles. Genetic variation will decline as alleles randomly go extinct. Allele frequencies will remain constant.

Genetic diversity at the locus under selection will decrease.

Consider a population undergoing positive selection for one allele at a diploid locus. The fitness advantage of this allele is moderate (s = 0.07). After many many generations, what outcome is most likely? Genetic diversity at the locus under selection will decrease. The allele with the lower fitness will mutate in response to selection for the other allele. Genetic variation will increase proportional to the population size. Both alleles will persist in the population because selection can change frequencies, but not eliminate alleles.

The beneficial allele will increase in frequency and eventually will be fixed by natural selection

Consider a population undergoing positive selection for one allele at a diploid locus. The fitness advantage of this allele is small (s = 0.001). After many many generations, what outcome is most likely? The beneficial allele will increase in frequency and eventually will be fixed by natural selection. Both alleles will remain in the population at a ratio proportional to the fitness difference. The population size will increase. The population size will decrease. The allele at a disadvantage will mutate to improve to the fitness level of the other allele.

The beneficial allele will increase in frequency and eventually will be fixed by natural selection.

Consider a population undergoing positive selection for one allele at a diploid locus. The fitness advantage of this allele is small (s = 0.007). After many many generations, what outcome is most likely if no other evolutionary forces are at play? The allele under selection will increase in frequency but will not go to fixation because the selection coefficient is so small. Both alleles will remain in the population at a ratio proportional to the fitness difference. The population size will decrease. The beneficial allele will increase in frequency and eventually will be fixed by natural selection. The allele at a disadvantage will mutate to improve to the fitness level of the other allele.

The population will eventually be fixed for A1B2C2.

Consider a region of the genome which has three loci (A,B,C) in close physical proximity on a chromosome, which undergo essentially no recombination during meiosis. A new mutant allele (B2) arises at locus B with a higher fitness than the ancestral B allele. The individual with the mutated B2 allele has this genotype: A1B2C2 Which of the following is likely to occur? There will be no change in allele frequencies because the loci are not recombining. Linkage disequilibrium at these 3 loci will contribute to increased levels of heterozygosity in the population. B2 will increase in frequency in the population due to positive selection and loci A and C will show high levels of polymorphism. The 3 loci will remain in linkage equilibrium and show polymorphisms due to random genetic drift. The population will eventually be fixed for A1B2C2.

Phenotypic variance should decrease as the selective environment changes and disfavors the previously bimodal distribution.

Consider the very real situation in which purple cone flower plants show continuous variation in flower color from light lilac to deep purple and adaptive fitness peaks occur when flower colors are at either extreme. The late-great musical artist formerly known as Prince's song "Purple Rain" became a reality, and that purple rain stuck to plants like paint. Pollinators can no longer easily find the deep purple flowers. How will the distribution of flower colors change in response to this new selective environment brought on by Purple Rain? Phenotypic variance should increase as the selective environment changes and disfavors the previously bimodal distribution. The historical disruptive selection would have reduced phenotypic variance to very low levels, which would impede evolution towards this new adaptive landscape. The historical stabilizing selection would have increased the frequency of intermediate colors so no changes in the distribution are expected under this new environment. Phenotypic variance should decrease as the selective environment changes and disfavors the previously bimodal distribution.

The highway severely blocks the southern population, allowing only a tiny amount of gene flow.

Florida panthers have undergone a severe bottleneck and habitat fragmentation caused by the construction of a major interstate highway. The effective population size on either side of the highway is about 75 and genome-wide scans show an Fst value of 0.19. How has the highway impacted this species? The highway completely isolates the southern population, allowing no gene flow. The highway only hinders migration a little bit and gene flow is maintained at a relatively high rate. The highway severely blocks the southern population, allowing only a tiny amount of gene flow. The highway is not a barrier to the cats at all, and the regions north and south of the highway act as a single, well-mixed population.

linkage disequilibrium; pleiotropy

Genetic correlations can have two causes: _______ and _______. linkage disequilibrium; epistasis linkage disequilibrium; pleiotropy phenotypic correlation; environmental correlation epistasis; pleiotropy phenotypic correlation; pleiotropy

relatively few individuals reproduce in a large population.

Genetic drift is likely change allele frequencies in a population when _________ large populations experience strong selection for a specific allele. the environment drastically changes over a short time scale and selection favors a previously infrequent allele. relatively few individuals reproduce in a large population. one allele confers a fitness benefit to individuals that have that allele versus those that do not.

level of genetic variation at the locus.

In a scenario where a population is evolving only in response to natural selection, allele frequencies will change at a rate proportional to the selection coefficient and the size of the population. population's growth rate. level of genetic variation at the locus. mean fitness of the population. degree of the allele's penetrance.

bottleneck.

In the late eighteenth century, a typhoon swept through the Pacific atoll of Pingelap, leaving approximately 20 human survivors. A large percentage of the present-day inhabitants of Pingelap are color blind. One can conclude, therefore, that the population experienced a bottleneck. selective sweep. coalescence. mutation. speciation event.

have loci in their genomes that evolve under drift, but at a lower rate than smaller populations.

Large populations with individuals that have equal chances creating offspring will _____ have lower genetic diversity than a smaller population. evolve traits faster than smaller populations because of drift. not experience drift because of the large population size. have loci in their genomes that evolve under drift, but at a lower rate than smaller populations.

a bimodal distribution with high frequencies of small and large rakes.

Our favorite fish, the three-spined stickleback uses "rakes" on it's gills to capture food from the water column or from the bottom sediments. Plankton are very small organisms that float in the water column and are an excellent food source. Blood worms found in sediments are also a great prey item and are relatively giant compared to plankton. Sticklebacks are polymorphic for the size of their gill rakes, but intermediate rake sizes fail to efficiently capture either prey type. What distribution would we expect to see for rake size if we measured many individuals? low variance around the mean rake size. a bimodal distribution with high frequencies of small and large rakes. a uniform distribution with equal amounts of individuals with small medium and large rakes A normal distribution with the majority of individuals showing intermediate rake sizes.

disruptive selection

Our favorite fish, the three-spined stickleback uses "rakes" on it's gills to capture food from the water column or from the bottom sediments. Plankton are very small organisms that float in the water column and are an excellent food source. Blood worms found in sediments are also a great prey item and are relatively giant compared to plankton. Sticklebacks are polymorphic for the size of their gill rakes, but intermediate rake sizes fail to efficiently capture either prey type. What type of selection would you predict acted on the ancestral population of sticklebacks? stabilizing selection positive selection disruptive selection

environmental variance.

Phenotypic variance that is not due to genetic variance can be attributed to linkage disequilibrium. dominance. environmental variance. pleiotropy. epistasis.

The alleles that confer high temp tolerance went to fixation. Despite selection imposed by researchers, there was no variation for selection to act on.

Populations of small crustaceans called Tigriopus copepods have experienced positive selection for alleles at multiple loci that encode high temperature tolerance over tens of 1000's of generations since it diverged from it's cooler-water ancestor. Researcher's want to test for the evolvability of high temperature tolerance in Tigriopus copepods, but find that experiments fail to result in increased temperature tolerance beyond their current capacity. What scenario best explains this constraint on evolution? High-temperature tolerance is an adaptation. Once adaptations evolve, they cannot be undone. The alleles that confer high temp tolerance went to fixation. Despite selection imposed by researchers, there was no variation for selection to act on. High temperature tolerance is not a heritable trait because it depends on the environment. Therefore no evolution can occur. Evolution cannot occur by artificial selection, only through the non-random process of natural selection.

a fitness advantage to phenotypes that are common.

Positive-frequency dependent selection results in ____________ a fitness advantage to phenotypes that are relatively rare in a population. the maintenance of polymorphism for the trait under selection. a fitness advantage to phenotypes that are common. an increase in heterozygosity at a locus under selection.

the effective population size, Ne.

The rate of evolution of an allele under positive selection is a function of all of the following EXCEPT the mode of inheritance of the alleles the strength of selection the effective population size, Ne. the amount of genetic variation in the population

Locus D shows signs of local adaptation because of its relatively high Fst. The Fst value of locus I indicates that the populations do not differ at this locus.

Refer to the graph. Ten variable loci were found in an island population of an organism. F ST was calculated for each to compare with the mainland population.What can we conclude from the data? (choose 2) The Fst value of locus I indicates a severe limit to gene flow between populations. All of the loci have undergone a high rate of adaptive evolution. Since the population is isolated, genetic drift has led to great differences when compared to the mainland. Locus D shows signs of local adaptation because of its relatively high Fst. Most loci have low Fst so there is probably not high migration between populations. The Fst value of locus I indicates that the populations do not differ at this locus.

Selective sweeps on standing variation results in more polymorphic loci nearby the locus under selection.

Selective sweep on standing genetic variation differs from a sweep on a newly mutated allele in which way? Sweeps on standing variation does not lead to hitchiking of other alleles but a sweep on a new allele does Sweeps on a new allele does not lead to hitchiking of other alleles but a sweep on existing variation does Selective sweeps on standing variation results in more fixation of alleles at loci nearby the locus under selection. Selective sweeps on standing variation results in more polymorphic loci nearby the locus under selection.

Genetic drift

Sewall Wright's metaphor of an "adaptive landscape" that includes "peaks" and "valleys" is used widely in evolutionary biology. Natural selection will always move populations' mean fitness up the peaks. Which influence is most likely to cause a population to move away from a fitness peak towards a valley? Purifying selection Large population size Overdominant selection Positive selection Genetic drift

there is a good match between most of the individuals' phenotype and the environment and the environment is stable

Stabilizing selection typically occurs when environmental conditions change stochastically over time there is a good match between most of the individuals' phenotype and the environment and the environment is stable there is a good match between most of the individuals' phenotype and the environment and the environment is changing Individuals with the extreme phenotypes have relatively high fitness

It acts as a barrier to gene flow and could cause large Fst values across the genome.

The Congo River formed about 1.5 million years ago and has acted as a barrier, preventing interbreeding by chimpanzees ( Pan troglodytes) and bonobos ( Pan paniscus). What effect does the river have? It acts as a barrier to gene flow and could cause large Fst values across the genome. It delayed the eventual speciation event because it blocked gene flow. Decreased the likelihood that each species would evolve local adaptations. It acts as a barrier to gene flow and prevented drift from accumulating genetic differences among the species. It caused alleles from each species to mix across populations.

A large amount of genetic variation observed among species is due to genetic drift acting on loci that don't affect fitness

The Neutral Theory of Molecular Evolution suggests that Genetic variation among species is nearly always due to positive selection for traits that are adaptive Highly deleterious alleles are those that contribute the biggest differences among species. A large amount of genetic variation observed among species is due to genetic drift acting on loci that don't affect fitness If a gene is evolving via drift it is not possible for selection to affect fixation or loss of its alleles.

heritability of the trait in question and the difference in the phenotype between adults who survived versus died after selection.

The amount of change expected in one generation following positive selection depends on ______ and _______ heritability of the trait in question and the population size standing genetic variation and the initial frequency of the alleles heritability of the trait in question and the difference in the phenotype between adults who survived versus died after selection. the total phenotypic variance and the location of the loci in the genome

Purifying selection on alleles that encode low respiratory capacity are in linkage disequilibrium with another alleles that encode traits associated with longer lifespan. Over generations, the population shows shorter longevity, but higher respiratory capacity.

The average value of a particular phenotype in a population can change despite selection not acting directly on that trait. Which scenario describes a mechanism that can produce this outcome? Purifying selection on alleles that encode low respiratory capacity are in linkage disequilibrium with another alleles that encode traits associated with longer lifespan. Over generations, the population shows shorter longevity, but higher respiratory capacity. Stabilizing selection for an optimal beak morphology decreases the variance of this phenotype in the population. Aphid insects produce a honeydew that contains dopamine, which ants feed on. As a result, the ants act more aggressively towards non-aphid insects. High rates of recombination segregate alleles that encode fruit size and alleles that encode drought resistance. The next generation of plants shows high phenotypic variance in these traits.

difference in population trait mean before and after selection.

The change in the average trait value of a population under selection is equal to the heritability multiplied by the selection differential. The selection differential is the difference in average number of offspring produced by each phenotype. variance in the measurements of the trait in the population. difference in relative fitness between members of the population with different genotype. percent change in likelihood of survival and reproduction. difference in population trait mean before and after selection.

both alleles are maintained in the population, and allele A 2 is more common than allele A 1.

The colors of individuals in a snail population are determined by a single autosomal locus. A 1 A 1 homozygotes are red, A 1 A 2 heterozygotes are pink, and A 2 A 2 homozygotes are white. Genotypic fitnesses are as follows: w A 1 A 1 = 0.5; w A 1 A 2 = 1.0; w A 2 A 2 = 0.75. At equilibrium, both alleles are equally frequent. both alleles are maintained in the population, and allele A 1 is more common than allele A 2. the population is fixed for allele A 2. the population contains only A 1 A 2 heterozygotes. both alleles are maintained in the population, and allele A 2 is more common than allele A 1.

Allele frequencies will converge on the allele frequency of the continent population.

The continent-island model of gene flow proposes that the movement of migrants from the continent to the island has a large effect on the island, but not the other way around. The only evolutionary force at play is gene flow. What is predicted to happen to allele frequencies of the island and continent populations if they started off at different frequencies? Allele frequencies will converge on the allele frequency of the continent population. Allele frequencies will converge on the average between the island and continent populations. The island allele frequency will not change but the continent population will see a decrease in allele frequency. Allele frequencies will remain constant on the island and the continent.

show a change in the mean value of the phenotype and maintain the amount of variation in the population.

The distribution of a quantitative phenotype in a population that experiences positive selection should show a change in the mean value of the phenotype and maintain the amount of variation in the population. include only individualwith very small or very large phenotype values contain fewer individuals with extreme phenotypes have the same average phenotype value, but show less variation than before selection

trade-offs.

The distribution of phenotypes in natural populations are not always aligned with the theoretical adaptive peak. What is one mechanism that could constrain phenotypes from evolving to adaptive peaks of the highest fitness? linkage disequilibrium. variable selection. trade-offs. selection on variance. realized heritability.

number of reproductive migrants that arrive in a population in a generation.

The product N e m is equal to the change in allele frequency in a population as a result of gene flow. number of reproductive migrants that arrive in a population in a generation. average distance between the birthplace of parent and offspring. width of a cline when selection and gene flow work against each other. migration variance.

zero because genetic diversity is zero

The rate of evolution at a single locus that goes to fixation for an allele Py is maximized when genetic diversity is 0.5 zero because genetic diversity is zero minimal because genetic diversity is high maximized because selection acts on fixed alleles only

Heritability drops towards zero because phenotypic variation is only contributed by environmental variance.

What happens to the heritability of a trait as the most fit allele in the population approaches fixation? Heritability increases as natural selection is relaxed. Heritability drops towards zero because phenotypic variation is only contributed by environmental variance. Heritability increases towards 1, following the frequency of the allele. The heritability is equal to the selection gradient for that locus. Heritability remains constant because all traits are still coded by genes passed from parent to offspring.

Characters with little genetic variation will constrain the rate of natural selection; correlated characters may increase in fitness less rapidly, because they can evolve only along the greatest axis of variation.

What is meant by the statement "Evolution may proceed along 'genetic lines of least resistance'"? The phenotypes produced by genes under selection will be those that require the least energy input, despite potential fitness gains. Characters with little genetic variation will constrain the rate of natural selection; correlated characters may increase in fitness less rapidly, because they can evolve only along the greatest axis of variation. Functionally correlated characters will not remain genetically correlated, because they are broken up during segregation and crossing over. Evolution operates on the set of phenotypes that a genotype can produce under all possible environmental conditions. Because mutations may be more likely to appear at some locations in a gene than at others, we can easily predict the phenotype it will experience when natural selection occurs.

Increased lifespan of planktonic larvae

What is most likely to increase rates of gene flow for a benthic (bottom dwelling) marine invertebrate? Greater maximum age reached by adults Expansion of territory size defended by breeding males Stronger natural selection for camouflage color patterns Increased lifespan of planktonic larvae An expansion in the breadth of diet

only genetic variance and environmental variation contribute to phenotypic variance.

When the environment affects the phenotypes of all the genotypes in a population and the reaction norms of the genotypes are parallel, phenotypic variation is driven by environmental variance only. phenotypic variance includes environmental variance, genetic variance, and a genotype by environment interaction. phenotypic variation is driven by a genotype by environment interaction only. only genetic variance and environmental variation contribute to phenotypic variance. phenotypic variation is driven by genetic variance only.

Advantageous mutations occur often, and many fixation events are due to positive selection.

Which assumption does not underlie Kimura's neutral theory of molecular evolution? Advantageous mutations occur often, and many fixation events are due to positive selection. Mutation rates affect rates of substitution. Deleterious alleles are eliminated by means of (purifying) natural selection. Evolutionary changes at the molecular level occur at a relatively constant rate.

An exon that codes for the active site of a protein enzyme

Which bit of genetic material would be least likely to evolve via drift. An exon that codes for the active site of a protein enzyme Nucleotides found at the first position of codons in an intron Second position nucleotides of codons in a pseudogene DNA in the centromere of a chromosome

The population is recovering from a bottleneck, which drastically reduced the amount of genetic variation in the population.

Which condition is most likely to account for a difference between the total population size and the effective population size ( N e) in a rapidly growing population of humans? The population is recovering from a bottleneck, which drastically reduced the amount of genetic variation in the population. There are frequent matings between full and half-siblings. Inbreeding is low or nonexistent. There are different numbers of males and females in the population. Population size fluctuates.

Individuals that are very successful at migrating to new populations, but cannot mate in the new locations

Which condition would result in the least evolution as a result of gene flow? Migration rates that vary greatly from year to year A great dispersal distance between birth and mating Individuals that are very successful at migrating to new populations, but cannot mate in the new locations Very different allele frequencies in different subpopulations Unusually high migration variance

The fraction of genetic variance in a group of populations that results from differences between them

Which is the best explanation for what F ST represents? A direct estimation of isolation-by-distance The variance of gene frequencies within a population compared to the variance of gene frequencies in another population The fraction of genetic variance in a group of populations that results from differences between them The average distance between the birthplaces of a parent and its offspring The fraction of individuals in a population that arrives from another population in each generation

Negative-frequency dependent

Which mode of selection preserves genetic variation at the locus under selection? Negative-frequency dependent Positive-frequency dependent Underdominance Positive Selection

A beneficial mutation in an extremely large population

Which mutation is most likely to become fixed? A beneficial mutation in an extremely large population A neutral or nearly neutral mutation in an extremely small population A beneficial mutation in an extremely small population All of these mutations are equally likely to be fixed. A neutral or nearly neutral mutation in an extremely large population

Low genetic diversity in a single population of a widely distributed species

Which observation would be the best evidence for a recent founder event or population bottleneck? Census evidence for a steadily growing population Evidence that population size on an island is maintained by a steady influx of migrants from the mainland Evidence that a specific genotype has a strong selective advantage in an environment Roughly equal genetic variation in all subregions of a species range Low genetic diversity in a single population of a widely distributed species

Mildly disadvantageous alleles can sometimes increase in frequency, due to genetic drift.

Which statement about genetic drift is true? Evolution by random genetic drift proceeds faster in large populations than in small populations. New mutations that are neutral are less likely to be fixed in small populations than in large populations. Mildly disadvantageous alleles can sometimes increase in frequency, due to genetic drift. Heterozygosity is unaffected by genetic drift.

drift and selection can cause differences to accumulate between populations, gene flow makes them more similar.

Which statement is correct? drift and selection can cause differences to accumulate between populations, gene flow makes them more similar. Gene flow and drift cause separate populations to accumulate genetic differences Selection can not lead to local adaptation in one population if there is gene flow with another population. gene flow, drift, and selection all lead to differences to accumulate between two separate populations.

Either strong selection or low migration

You observe a very narrow cline in the middle of a broadly distributed species' range. From this you could conclude that Either strong selection or low migration selection is strong. migration is low. migration is high. Either strong selection or high migration