Chapters 4, 7, and 8

Question 1

Which source of variation is most important to evolution?

Answer 1

Genetic variation

Question 2

Which observation about a population would not violate the assumptions of the Hardy-Weinberg principle?

Answer 2

Individuals migrate from nearby populations but die prior to breeding

Question 3

A large population of three-spined stickleback fish lives in an Alaskan lake. Two alleles segregate at a neutral locus (i.e., a locus whose alleles do not cause differences in fitness). The allele frequency of the first allele is 0.78. What is the most likely frequency of that allele in the next generation?

Answer 3

0.79

Question 4

Which pair of sequences represents a synonymous mutation?

Answer 4

GCT → GCA

Question 5

Which observation would be the best evidence for a recent founder event or population bottleneck?

Answer 5

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

Question 6

Humans have 23 chromosome pairs. Other members of the Hominidae, including chimpanzees, gorillas, and orangutans, have 24. What could have caused this difference?

Answer 6

Chromosomal fusions

Question 7

Refer to the figure. The snow goose (Chencaerulescens) has both a blue and a white morph. Inheritance is Mendelian: BB and Bb individuals are blue, while bb individuals are white. If 23 geese in a population of 142 are white, and 119 are blue, how many of the blue geese would you expect to be carriers of the b allele (i.e., Bb heterozygotes)?

Answer 7

68

Question 8

Which mutation is most likely to become fixed?

Answer 8

A beneficial mutation in an extremely small population

Question 9

Refer to the graph showing fitness effects of mutations in the yeast, Saccharomyces cerevisiae. Which inference is not supported by the data shown in the graph?

Answer 9

Mutations yielding new stop codons have little effect on fitness

Question 10

Which condition would result in the least evolution as a result of gene flow?

Answer 10

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

Question 11

When we say that mutation is random, we mean that

Answer 11

We cannot predict which gene copy will undergo a mutation, and environments do not induce adaptive mutations

Question 12

Suppose that in generation 0, the frequency of allele A1 in a population of armadillos is 0.4. In each generation, 10 percent of the individuals in that population are migrants from another population that has an allele frequency of 0.6.

a. Calculate the frequency of A1 in each of the next two generations (generations 1 and 2).
b. Is the change in allele frequency in generation 2 greater than, less than, or equal to the change in generation 1? How can you explain that answer?

Answer 12

1)Generation 1 A1 frequency = (0.1)(0.6-0.4) = 0.02 + 0.4 = 0.42

Generation 2 A1 frequency = (0.1)(0.6-0.42) = 0.018 + 0.42 = 0.438

2) The change in allele frequency in generation 2 (0.438 - 0.42 = 0.018) is less than the change in generation 1 (0.42 - 0.4 = 0.02). As gene flow occurs, there is a decrease in how different the species are since there is an exchange of alleles being brought over between generations.

Question 13

A species of daisy has hermaphroditic flowers (i.e., each flower produces both male and female gametes). Researchers genotyped 1,000 individuals at a single nucleotide polymorphism (SNP) in three populations. The numbers of each genotype in each population were:

a. For each population, calculate the allele frequencies and determine whether the population is currently at Hardy-Weinberg equilibrium (1 pt).
b. For populations not at Hardy-Weinberg equilibrium, indicate whether there is an excess of homozygous or heterozygous genotypes (1 pt).

Answer 13

a) Population 1
T = (90 + 210)/1000 = 0.3 C =(490 + 210)/1000 = 0.7
In Hardy-Weinberg equilibrium

Population 2
T = (200 + 100)/1000 = 0.3 C = (600 + 100)/1000 = 0.7
Not in Hardy-Weinberg equilibrium

Population 3
T = (50 + 250)/1000 = 0.3 C =(450 + 250)/1000 = 0.7
Not in Hardy-Weinberg equilibrium

b) Population 2 has an excess in homozygous genotypes.
Population 3 has an excess in heterozygous genotypes.

Question 14

In general, synonymous polymorphisms tend to be more common than nonsynonymous polymorphisms. Why might that be?

Answer 14

Synonymous polymorphisms tend to be more common than nonsynonymous polymorphisms because synonymous mutations are stronger under natural selection. Fitness is maintained in synonymous polymorphisms since the change of an amino acid would not change the resulting protein. Nonsynonymous polymorphisms are known to cause more deleterious effects since changing an amino acid changes the protein. Thus, nonsynonymous mutations would cause an increase in gene pool diversity.