Question 1

You are studying a population of 100 flowers that has two alleles at a locus for flower color, blue (B) and green (G). There are 15 individuals with the BB genotype, 70 individuals with the BG genotype, and 15 individuals with the GG genotype.
(a) What are the allele frequencies of B and G in the starting population? Show your calculations.
(b) Is this population in Hardy-Weinberg equilibrium? Show your calculations.
(c) Given the results of part b and the distribution of genotypes, offer a hypothesis that could explain the results. Explain your reasoning.

Accepted Answer

The answer of You are studying a population of 100...

Question 2

Below you see graphs that depict the change in frequency of a neutral allele in four populations that differ in size. Which population would you predict is the smallest?

Accepted Answer

The answer of Below you see graphs that depict the...

Question 3

Genetic drift

Accepted Answer

A)  reduces genetic variation within a population. 
B)  increases divergence (variation) between populations. 
C)  affects only neutral alleles. 
D)  a and b 
E)  a, b, and c

Question 4

In which of the scenarios below is a population more likely to evolve?

Accepted Answer

A)  a population that experiences no migration 
B)  a population that is large enough to not experience genetic drift 
C)  a population where there are no adaptive traits 
D)  a population that experiences a mutation in a gene necessary for survival

Question 5

Many plant species are hermaphroditic and run the risk of self-mating. Some species carry self-incompatibility alleles that can prevent this from occurring. If a pollen grain with self-incompatibility allele S1 lands on a stigma that also carries the S1 allele, the pollen will not germinate and fertilization does not occur. Thus, this mechanism not only prevents selfing, but also has the unfortunate effect of preventing mating with any other plant that carries the same allele. However, if the pollen lands on a stigma of a plant with a different allele, fertilization occurs. Imagine a population of plants in which the allele frequency of S1 = 0.9 and the allele frequency of S2 = 0.1. All other things being equal, individuals with the ____ allele will have higher fitness on average. This is an example of ______.

Accepted Answer

A)  S1; positive selection 
B)  S2; positive selection 
C)  S1; negative frequency-dependent selection 
D)  S2; negative frequency-dependent selection

Question 6

Inbreeding

Accepted Answer

A)  changes allele frequencies in a population. 
B)  rearranges allele combinations in a population. 
C)  is a mechanism of evolution. 
D)  all of the above

Question 7

Tasmanian devils once inhabited most of present-day Australia, but only an isolated population on the island of Tasmania has survived to the present day. Which of the following processes has likely affected Tasmanian devils as a result of this history?

Accepted Answer

A)  a higher mutation rate 
B)  stronger natural selection 
C)  a genetic bottleneck 
D)  gene flow

Question 8

The frequency of a slightly deleterious allele maintained at an equilibrium frequency by mutation-selection balance would be higher

Accepted Answer

A)  if the mutation rate is high. 
B)  if the mutation rate is low. 
C)  if the selection coefficient is high. 
D)  if the population size is small.

Question 9

The graph below shows the change in allele frequency for a beneficial allele over time (the x axis shows generations). Based on the shape of the curve, this allele is most likely

Accepted Answer

A)  homozygous. 
B)  dominant. 
C)  recessive. 
D)  heterozygous. 
E)  additive.

Question 10

Alleles are

Accepted Answer

A)  found at genetic loci. 
B)  always dominant or recessive. 
C)  alternative forms of a phenotype. 
D)  a and b 
E)  a, b, and c

Question 11

In a population of butterflies that has two alleles at a locus for spots, no spots (N) and spots (S), there are 20 individuals with the NN genotype, 40 with the NS genotype, and 40 with the SS genotype. What is the frequency of N in the population?

Accepted Answer

A)  0.4 
B)  0.2 
C)  0.6 
D)  0.8 
E)  none of the above

Question 12

Bighorn sheep occupy a range that extends from Canada to Mexico; however, this range is not continuous because the sheep prefer steep rocky cliffs, which are often spatially isolated. This is an example of

Accepted Answer

A)  population structure. 
B)  population genetics. 
C)  allopatry. 
D)  genetic distance.

Question 13

How does "random mating" affect population genetics studies?

Accepted Answer

A)  Random mating only relates to the locus of interest, so sexual selection often does not affect population genetics studies. 
B)  Individuals never have a strong mate preference, so they frequently mate with any "random" individual. 
C)  Individuals always have a strong mate preference, so population genetics studies are almost always biased. 
D)  none of the above

Question 14

Assuming that a deleterious allele is maintained in a population by mutation-selection balance, which scenario below describes the case where you would expect the equilibrium frequency of the allele to be highest?

Accepted Answer

A)  The mutation rate is low; the allele is highly deleterious. 
B)  The mutation rate is low; the allele is slightly deleterious. 
C)  The mutation rate is high; the allele is highly deleterious. 
D)  The mutation rate is high; the allele is slightly deleterious.

Question 15

The study of allele frequencies and distributions is

Accepted Answer

A)  population genetics. 
B)  community dynamics. 
C)  biogeography. 
D)  landscape ecology.

Question 16

You collect the following data on genotypes for a sunflower population: AA: 40, AB: 20, BB: 40. Based on Hardy-Weinberg predictions you expected the following numbers: AA: 25, AB: 50, BB: 25. Which of the following is a plausible explanation for the deviation?

Accepted Answer

A)  balancing selection 
B)  negative frequency-dependent selection 
C)  inbreeding 
D)  genetic drift

Question 17

Which of the following is not true about a fixed genetic locus?

Accepted Answer

A)  All members of a population carry the same allele for that locus. 
B)  There is no genetic variation for that locus. 
C)  All alternative alleles for that locus have disappeared. 
D)  all of the above 
E)  none of the above

Question 18

How might population structure affect evolution?

Accepted Answer

A)  increases the opportunity for selection to change allele frequencies 
B)  decreases the opportunity for selection to change allele frequencies 
C)  increases the opportunity for drift to change allele frequencies 
D)  decreases the opportunity for drift to change allele frequencies

Question 19

In the founder effect,

Accepted Answer

A)  allele frequencies always deviate from the parental population. 
B)  drift only acts on the founding population when it breaks off from the parental population. 
C)  drift may continue to act on a fledgling population. 
D)  a and b 
E)  a and c

Question 20

If p = 0.8, what is the frequency of heterozygotes in a population, assuming Hardy-Weinberg equilibrium?

Accepted Answer

A)  0.2 
B)  0.64 
C)  0.16 
D)  0.32 
E)  none of the above

Exam 6: The Ways of Change: Drift and Selection