exam 2: evolution in finite pop

Question 1

Genetic drift causes changes in

Answer 1

the frequency of heterozygotes in a population to decrease over time

the change in frequency of an existing gene variant in the population due to random chance.

*allele frequencies

Question 2

Genetic drift is caused by ________ processes

Answer 2

random

Question 3

The two graphs show the change in allele frequency, p, over 100 generations. Each graph
shows 10 diƯerent populations, all experiencing the same evolutionary forces. What is the
most likely diƯerence between the populations shown in the top graph compared to the
populations in the bottom graph

Answer 3

The population sizes in the graph on top are smaller than the population sizes in the graph on the bottom.

Question 4

What is the eƯect of small population size on the degree of heterozygosity in a
population?

Answer 4

Heterozygosity will decrease over time.

Question 5

The eƯective population size is often lower than the census size of a population because

Answer 5

ndividuals contribute unequally to future generations.

Question 6

Imagine an island archipelago where all of the islands are founded by individuals
heterozygous at a particular locus. If there is no migration or mutation, and the alleles at
that locus are neutral, what do you expect the island populations to look like after many
generations?

Answer 6

Some island populations will have fixed one allele, and other populations will have fixed the other allele.

Question 7

Population bottlenecks can result in rapid fixation or loss of alleles in otherwise large
populations because the bottleneck

Answer 7

reduces the effective population size

Question 8

Population bottlenecks occur when

Answer 8

a consistently large population experiences a brief period of small size.

Question 9

Which of the following is an example of a population bottleneck?

Answer 9

A large population of frogs is greatly reduced due to a drought.

Question 10

A founder event changes allele frequencies because

Answer 10

only a subset of alleles in the original population are represented in the newly founded population

Question 11

The neutral theory of molecular evolution posits that most mutations are ________ and
most substitutions are ________.

Answer 11

deleterious; neutral

Question 12

Refer to the figure of the genetic code shown to answer the following question.
Which of the following mutations to a codon is most likely to be selectively neutral

Answer 12

UUG → CUG

Question 13

The figure shows the Ka /Ks values for two regulatory genes in pairs of species in (A)
North American tarweeds and (B) Hawaiian silverswords. The dashed lines are the mean
Ka/Ks values. What do these data indicate about how these genes are evolving diƯerently in
these two groups of taxa?

Answer 13

They have experienced purifying selection in the tarweeds and positive selection in the silverswords.

Question 14

The molecular clock has limited usefulness for estimating divergence times among
species in part due to the saturation of DNA sequences. This occurs because

Answer 14

n highly diverged lineages, substitutions will occur at sites that have been substituted previously.

Question 15

The nearly neutral theory predicts that substitution rate is

Answer 15

higher in smaller populations.

Question 16

What is one reason that in small populations, the realized frequencies of alleles are not
as close to the expected frequencies

Answer 16

genetic drift

Question 17

If nonsynonymous changes occur more frequently than synonymous changes in a gene,
this suggests that

Answer 17

the gene may be under positive selection.