Unit 5 Review
1. Define the following terms:
a. Ernst Mayr
b. Biological species concept
c. Allopatric speciation
d. Sympatric speciation
e. Gradualism
f. Punctuated equilibrium
g. Prezygotic isolating
mechanism
h. Postzygotic isolating
mechanism
Use the following information to answer questions 2 – 5: A virus wipes out all the
waterfowl in a New Zealand watershed and temporarily removes the opportunity for the
trematode Microphallus parasite living in ponds in this area to reproduce sexually and
complete its life cycle. In response, a few Microphallus genotypes produce a mutation
that allows them to mature in their snail host and grow asexually for repeated
generations. Many generations later, you discover this population and become
interested in comparing the asexual population and a nearby population of Microphallus
with alternating sexual and asexual generations. Consider the predictions you might
make about the relative fitness of the asexual population compared to the population
with alternating generations.
2. Why might you expect the population with sexual reproduction to have higher fitness
in the long run?
3. What conditions might favor the asexual population?
4. You bring the individuals from the two populations into the lab, collect gametes, and
succeed in producing hybrid zygotes. However, very few of the fertilized eggs develop
into viable adults. Describe a genetic mechanism potentially responsible for this result.
5 Name one other mechanism that might prevent formation of hybrids if the two
populations were to come back into contact in the wild.
6. For each of the fictional examples given below, name the type of isolation mechanism
that is operating (be specific—don’t just say “pre-” or “post-zygotic”).
a. Western deer mice are unable to interact or mate with eastern deer mice,
because the Mississippi River divides them.
b. Brain corals and fan corals both release gametes (sperm and eggs) into the
water at night, but the two do not come into contact, because brain corals release
gametes when the moon is full and fan corals when the moon is dark.
c. Lollipop shrimp males would try to mate with candy cane shrimp females, but
the lollipop males’ claws are not the right shape to hold the candy cane females
during courtship/mating.
D. Bullfrog males will try to mate with just about anything, including rocks (this is
true). But when they fertilize the eggs of tree frog females, the developing
tadpoles die before they reach adulthood.
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7. Label each of the following examples as “Prezygotic Isolating Mechanism” or
“Postzygotic Isolating Mechanism.”
a. Zygote mortality
b. Temporal
c. Hybrid inviability
d. Hybrid breakdown
e. Gametic Isolation
f. Habitat
g. Behavioral
h. Hybrid sterility
i. Mechanical
8. Match the reproductive isolating mechanism with its definition.
ISOLATING
MECHANISM
a. Habitat/Geographical
b. Temporal
c. Behavioral
d. Mechanical
e. Gametic
f. Zygote mortality
g. Hybrid inviability
h. Hybrid sterility
i. Hybrid breakdown
DEFINITION
ANSWER
Differences in sex organ
embryo forms but viability is reduced
Behavior does not elicit mating
fertilization occurs zygote does not develop
hybrid offspring are sterile
Mate at different times
Occupy different geographic areas
first generation infertile but subsequent generations
are sterile
failure of sperm to meet egg
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