Deck 9: Evolution at Multiple Loci

Question 1

Consider a population with two loci (A, B), each with two alleles (A, a; B, b). What are the allele frequencies in this population if the haplotype frequencies are AB = 0.35, Ab = 0.15, aB = 0.35, ab = 0.15?

A) A =0.5, a = 0.5, B = 0.7, b = 0.3
B) A =0.7, a = 0.3, B =0.5, b =0.5
C) A = 0.6, a = 0.4, B = 0.7, b = 0.3
D) A = 0.5, a = 0.5, B = 0.6, b= 0.4

Answer 1

A =0.5, a = 0.5, B = 0.7, b = 0.3

Question 2

The figure shown demonstrates the genotypic adaptive landscape for bacteria growing in media without antibiotics. The height of the bars associated with a genotype indicates the fitness of that genotype. The R allele confers resistance to antibiotics, and the C allele compensates for the loss of fitness that the R allele confers in the absence of antibiotics. The rc haplotype lacks both compensation and resistance. Based on this landscape, why are resistance and compensation unlikely to be lost even in the absence of antibiotics?

A) A lack of mutation will prevent the haplotypes from changing.
B) Epistasis will maintain haplotype frequencies.
C) Haplotype frequencies do not change in Hardy-Weinberg populations.
D) RC populations are stuck on a local maximum.

Answer 2

D

Question 3

The statistical association of alleles at different loci is referred to as

A) linkage disequilibrium.
B) Hardy-Weinberg equilibrium.
C) epistasis.
D) linkage equilibrium.

Answer 3

A

Question 4

Which of the following is most likely to break up linkage disequilibrium?

A) drift
B) selection
C) mutation
D) recombination

Question 5

Hardy-Weinberg at two loci The figure demonstrates Hardy-Weinberg frequencies at two loci. Which term represents the expected offspring haplotype frequencies for a cross between parents with aB and aB gametes?

A) uv
B) u²
C) tu
D) t²

Question 6

The rediscovery of Mendelian inheritance caused increased scrutiny of Charles Darwin's theory of natural selection because of an apparent conflict in the two concepts. This conflict was based on the observation that Darwin focused on continuous traits, whereas Mendelian genetics deals with

A) discrete characters.
B) alleles.
C) garden pea plants.
D) genotypes.

Question 7

What is one reason why antibiotic resistance does not always disappear as quickly as one might expect after large-scale antibiotic use is ended?

A) Compensatory mutations arise at other loci in resistant bacterial strains, which eliminate fitness costs associated with the resistant phenotype.
B) Horizontal gene transfer occurs from other resistant bacterial strains.
C) Alleles for antibiotic resistance confer no fitness costs.
D) Alleles for antibiotic resistance confer no fitness benefits.

Question 8

Narrow-sense heritability is defined as the ________ genetic variation divided by the ________ variation.

A) total; total phenotypic
B) additive; total phenotypic
C) dominance; total phenotypic
D) additive; total dominance

Question 9

What is the largest possible value that linkage disequilibrium can reach if all allele frequencies are 0.5?

A) 0.25
B) 0.5
C) 0.75
D) 1

Question 10

What two major concepts in biology were unified in the middle of the twentieth century?

A) natural selection and genetic drift
B) discontinuous and continuous variation
C) mutation and migration
D) natural selection and Mendelian genetics

Question 11

Consider two loci located close together on a single chromosome. These loci

A) carry alleles that will never segregate together.
B) are physically linked.
C) are in linkage equilibrium.
D) are likely to be broken up during recombination.

Question 12

A haplotype is

A) all of the alleles at a single locus.
B) a product of epistasis.
C) a set of alleles at different loci along a chromosome.
D) all of the alleles in a population.

Question 13

Genotypic adaptive landscapes may better represent true adaptive landscapes than phenotypic adaptive landscapes when

A) single mutations can have a large effect on the phenotype.
B) phenotypic landscapes are hard to mathematically model.
C) phenotypic landscapes do not account for drift.
D) genotypic landscapes are easier to visualize.

Question 14

In quantitative genetic terms, a phenotypic value can be expressed as

A) dominant or recessive.
B) epistasis and pleiotropy.
C) genotypic value and environmental deviation.
D) selection differential and selection response.

Question 15

Which of the following occurs when there is so much Mendelian variation within a population that not all possible genotypes could be represented in any given generation?

A) epistasis
B) natural selection
C) latent variation
D) pleiotropy

Question 16

Assuming the value of linkage disequilibrium (D) is positive, recombination will generate

A) more repulsion pairs.
B) more coupling pairs.
C) no change, since recombination does not change expected haplotype frequencies.
D) an increase in the value of D.

Question 17

Which of the following processes that can create linkage disequilibrium is illustrated in the figure?

A) drift
B) selection
C) mutation
D) migration

Question 18

If the value of linkage disequilibrium (D) is equal to -0.25, one can infer that the alleles are

A) in repulsion.
B) in coupling.
C) not interacting.
D) interacting but only mildly with little effect on disequilibrium state.

Question 19

Selection can generate novel phenotypes by

A) drift causing the creation of a new phenotype.
B) increasing the probability of novel allele combinations.
C) genetic hitchhiking and selective sweeps.
D) creating linkage disequilibrium.

Question 20

The observation of an offspring phenotype outside of the range of parental phenotypes is most likely due to

A) additive genetic effects.
B) mutation.
C) genetic drift.
D) latent variation.

Question 21

Broad-sense heritability is defined as the ________ genetic variation divided by the ________ variation.

A) total; total phenotypic
B) additive; total phenotypic
C) dominance; total phenotypic
D) additive; total dominance

Question 22

When the alleles at two or more loci interact in nonadditive ways, we refer to this as

A) pleiotropy.
B) epistasis.
C) physical linkage.
D) linkage equilibrium.

Question 23

In a population of dragonflies, wing structure is determined by two loci (A, B), each with two alleles (A and a, B and b). Abnormal wings are produced in aa individuals unless they possess at least one B allele. This is an example of what evolutionary phenomenon?

A) epistasis
B) linkage equilibrium
C) physical linkage
D) latent variation

Question 24

Consider two microsatellite loci (A, B), each with two alleles determined by the number of repeats of the microsatellite motif (A = 15 or 17; B = 27 or 31). You genotype an individual in this population and determine that its haplotype is 15/27 and 15/27. Are these alleles in coupling and/or repulsion? Explain your answer.

Question 25

What is narrow-sense heritability and why is it a useful metric?

Question 26

In Lake Malawi cichlid fish, one can observe two color variants, Black Barred (BB) and Orange Blotch (OB). Sex in these fish is not determined by a sex chromosome but by a gene on an autosome, which produces either males or females. Both of these phenotypes are controlled by one biallelic locus each. OB females have a selective advantage in terms of their survivability: the OB phenotype allows females to blend into their background. OB males have a selective disadvantage because their reproductive coloration is disrupted and they have little mating success. How would this process influence the association of alleles at the color locus and sex-determining locus?

Question 27

An individual mapped within an adaptive landscape as a point located in a fitness valley would be characterized as having

A) high fitness.
B) low fitness.
C) a fitness peak.
D) a single-peaked landscape.

Question 28

Which of the following reflects the degree to which offspring resemble their parents in a population?

A) narrow-sense heritability
B) broad-sense heritability
C) selection differential
D) dominance

Question 29

Which of the following processes causes a neutral allele to increase in frequency because it is linked to an allele under selection?

A) mutation
B) genetic drift
C) genetic hitchhiking
D) background selection

Question 30

If we are interested in the A, B, and C loci of a diploid organism, which of the following would be a possible haplotype?

A) ABc
B) AABbcc
C) Aa
D) AAcc

Question 31

Which of the following does NOT represent a way in which genotype and phenotype can interact?

A) pleiotropy
B) epistasis
C) norms of reaction
D) physical linkage

Question 32

The phenotypic variation created by random chance events during the process of an organism's development is called

A) mutation.
B) drift.
C) acclimation.
D) developmental noise.

Question 33

Consider two loci (A, B), each with two alleles (A and a, B and b, respectively). The frequency (f) of A is known to be 0.30, the frequency (f) of b is known to be 0.25, and the coefficient of linkage disequilibrium (D) between loci A and B is known to be 0.15. What is the expected haplotype frequency of h_aB? Use the equation D =f_af_B -h_aB to solve. Show your work.

Question 34

Using the concept of adaptive landscapes, explain why a population may never reach its most fit phenotype.

Question 35

If recombination between locus A and locus B (r) is 0.15, and the initial value of linkage disequilibrium (D) is 0.20, what will the value of linkage disequilibrium be after one generation of recombination? Show your work.

Question 36

Multiple drug-resistant Staphylococcus aureus (MRSA) is a bacterium that has developed resistance to a wide range of antibiotics. Its resistance to penicillin, methicillin, and oxacillin is a result of the serial use of these antibiotics, which created a selective environment that favored resistance to the drug being used at the time. This resistance provides the bacteria with the ability to thrive in an environment with standard antibiotics, thereby making it a dangerous human health hazard. Why might one expect MRSA to retain penicillin resistance even if this antibiotic is rarely used?

Question 37

When the alleles at all loci of interest occur independently, what will the value of linkage disequilibrium (D) be?

A) 1
B) 0
C) -0.25
D) 0.25

Question 38

A researcher tracks the escape behavior of a population of squirrels on campus across two generations. When she plots the escape behavior of the offspring generation against the parental behavior, she notes that the offspring's behavior exactly matches the parental behavior. Nonetheless, the narrow-sense heritability equals zero. How can the heritability equal zero in this example?

A) The additive genetic variance equals one.
B) All the escape behavior alleles are fixed in the population.
C) Phenotypes vary widely between generations.
D) Escape behavior is controlled by a rare recessive allele.

Question 39

A species of lotus produces a nearly continuous spectrum of flower colors, ranging from white to deep red. The color of the flower is determined by 10 loci, each with two codominant alleles. What concept does this example illustrate?

Question 40

In the figure depicting heritability of migratory timing in the blackcap warbler, what does the straight line indicate?

A) the broad-sense heritability
B) the narrow-sense heritability
C) the norm of reaction of nocturnal restlessness
D) the response to selection

Question 41

Without using mathematical symbols, explain the difference between broad- and narrow-sense heritability, including why one is more relevant to evolutionary studies.

Question 42

Explain why one cannot compare the estimated heritability of fin length from different populations of the same fish species located in different lakes.

Question 43

Name three selective consequences of genetic linkage.

Question 44

Why would we expect genotypic adaptive landscapes to have rugged contours?

Question 45

What processes generate, and what processes remove, linkage disequilibrium?

Question 46

What would a map of phenotype space look like?

Question 47

A study of susceptibility to major depressive disorder in monozygotic twins separated at birth revealed that the broad-sense heritability of this trait is 0.10, and its total phenotypic variance is 0.25. What is the variance of the genotypic value of this disorder? Show your work.