A24fiffAnswers
Figure 12.14
Q1: Why do you think a genetic bottleneck is more likely to occur
in a small population than in a large population?
A1: In a large population, it is less likely that a chance event can
kill off almost all of the individuals, leaving only a few behind
that randomly represent only one of multiple phenotypes. In a
small population, a tsunami, hurricane, volcanic eruption, or
other natural disaster could easily kill off all but a few individuals.
All subsequent offspring would arise from these few individuals,
whatever phenotype they might have, regardless of which
phenotypes in the original population were best adapted.
Q2: Genetic drift is often described as a “chance event.” Give other
examples of chance events that could cause a genetic bottleneck.
A2: Examples that could cause a genetic bottleneck include deadly
viruses, famine, drought, immigration of many predators, habitat
loss, tsunami, or other natural disaster.
Q3: Which resulting population has more genetic diversity?
A3: The population on the left.
CHAPTER 13
END-OF-CHAPTER ANSWERS
- b
- a
- c
- c
- genetic divergence, allopatric
- Postzygotic barriers, an infertile hybrid
- d
- b, c, d
- (a) 5, (b) 4, (c) 1, (d) 2, (e) 3
- b
- b
- Any large geographic barrier such as a river, canyon, or moun-
tain range might bring about allopatric speciation. In addition
to the barrier, genetic divergence between the separated popu-
lations is necessary for speciation.- The ten species must have differed significantly in traits that
were unobservable (or at least were not observed by the scien-
tists) and that meant the fish were unable to mate and produce
viable offspring.ANSWERS TO FIGURE QUESTIONS
Figure 13.4
Q1: How do we know that these rattlesnakes are members of the
same species?
A1: The caption specifies that they successfully mated and the
resulting offspring survived and reproduced.Q2: How would you design an experiment to determine whether
two populations are distinct species according to the biological
species concept?A2: Your experiment would require mixing individuals from
the two populations under conditions conducive to sexual
reproduction. If the individuals did mate, the offspring would
then need to be raised to maturity and be set up to also mate and
produce live offspring.Q3: For which types of populations does the biological species
concept not work as a way of determining how they are related?A3: Because it requires sexual reproduction, the biological species
concept cannot be applied to populations that reproduce asexually
(such as bacteria).Figure 13.5
Q1: List three kinds of information that scientists use to
distinguish between species.A1: Biogeographic information, DNA sequence similarity, and
physical characteristics.Q2: What differences can you observe between the individuals in
the photos? Why are these differences not enough to confirm that
they are from two different species?A2: There are several striking differences in coloration (for
example, along the side of the body) between the frogs in the two
photos. These differences could simply be within-species variation,
much like hair and eye color differences between humans of the
same species.Q3: How is genetic divergence among populations determined?A3: Genetic divergence between two populations is determined by
examination of the DNA sequences of many individuals in the two
populations. A lot of similarity between DNA sequences suggests
little genetic divergence, while the existence of many changes
between the gene sequences suggests much greater genetic
divergence.Figure 13.6
Q1: What is the definition of gene flow? How was gene flow
blocked between these species?A1: Gene flow is defined as the passing of alleles between different
populations of the same species. Squirrels from the populations on
either side of the river could not mate because of the geographic
barrier, and thus gene flow was blocked.Q2: Name as many types of geographic barriers as you can. Which
do you think would be the best at blocking gene flow?A2: Examples of geographic barriers include but are not limited
to rivers, lakes, oceans, glaciers, mountains, canyons, brick walls,
freeways, fences. The larger the barrier, the better it blocks two
individuals from finding each other and mating.Q3: Are geographic barriers universal for all species? If not, name
a geographic barrier that might block gene flow for one species but
not another.