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1.2 C: Evidence for Evolution via Natural Selection Quiz
1.
A pesticide that was rarely used in 1932 was used with increasing frequency until it was banned
altogether by 1972. Fruit flies (Drosophila melanogaster) that are resistant to this pesticide carry
the r allele. The table below shows the frequency of the r allele in a population of fruit flies over
time.
In 2011, 3% of fruit flies were homozygous for the r allele. Which statement best predicts how the
frequency of the r allele will change in future generations of fruit flies?
(A) The frequency of the r allele will increase until the population reaches genetic equilibrium
because more individuals are heterozygous than homozygous recessive.
(B) The r allele will become less common in the population because there is a selective
advantage for the dominant and heterozygous phenotypes.
(C) The r allele will become more common in the population because fewer flies in the
population than expected have the recessive phenotype.
(D) The frequency of the r allele will remain stable because the population has already
reached genetic equilibrium.
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1.2 C: Evidence for Evolution via Natural Selection Quiz
2.
The majority of Eastern gray squirrels (Sciurus carolinensis) have gray fur, but a small percent of
the population have black fur. The percent of squirrels with black fur is less in the deciduous
forests of the United States, where trees lose their leaves in winter, and is greater in northern
coniferous forests, where conifer trees keep their needles throughout the winter, producing a
dark forest floor.
Which statement best explains the higher percent of squirrels with black fur in northern
coniferous forests than in deciduous forests?
(A) Individual squirrels in coniferous forests adapted to the forest floor and gradually changed
their fur to a slightly darker color. Over time, the darker squirrels passed on the darker trait,
and the squirrels’ fur became black over many generations.
(B) The coniferous forests contain small, isolated populations of squirrels, and the allele for
black fur became prevalent due to a combination of limited genetic diversity and genetic
drift.
(C) Squirrels with black fur in coniferous forests have a selective advantage over squirrels with
gray fur, and these squirrels were able to pass the trait for black fur on to more offspring
than the black squirrels in the deciduous forests.
(D) The number of mutations creating the black fur allele is higher in coniferous forests than in
deciduous forests. This has created a higher allelic frequency for the black fur allele,
allowing for greater expression of the black phenotype.
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1.2 C: Evidence for Evolution via Natural Selection Quiz
3.
Green crabs are native predators of the blue mussels that live along the coast of Maine. The
blue mussels have acquired an adaptation that allows them to detect the unique waterborne
chemicals produced by green crabs and produce thicker shells that are more difficult for the
green crabs to break.
In 1990, the Asian shore crab was introduced to the southern coast of Maine. As of today, Asian
shore crabs have not migrated to the waters off northern Maine. Asian shore crabs are more
aggressive than green crabs, and were able to break the thicker shells the mussels developed in
response to the green crabs. Scientists were amazed to find that in just 15 years after the
introduction of Asian shore crabs in the south, most of the blue mussels along the southern
coast of Maine have developed even thicker shells that are difficult for the Asian shore crab to
break. Scientists hypothesize that the southern mussels acquired the ability to detect and
respond to the waterborne chemicals produced by the Asian shore crab.
To test this hypothesis, scientists conducted an experiment to determine the effect of the
waterborne chemicals produced by Asian shore crabs on southern and northern blue mussels.
Southern and northern blue mussels were exposed to the unique waterborne chemicals
produced by green crabs and Asian shore crabs for three months. The complete results of the
green crab experiment and partial results of the Asian shore crab experiment are shown below.
Which statement best predicts how the northern mussels will respond when they are exposed to
the unique waterborne chemicals released by Asian shore crabs?
(A) There will be no change in the shell thickness of northern mussels because the majority of
individuals do not have an adaptation to detect and respond to the unique chemicals
released by Asian shore crabs.
(B) The majority of northern mussels will have a slight increase in shell thickness, but they will
not produce shells as thick as those of the southern mussels because they have had less
time to learn how to respond to the new predator.
Continued on next page
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1.2 C: Evidence for Evolution via Natural Selection Quiz
Continued from previous page.
(C) The majority of northern mussels will have a rapid increase in thickness because these
individuals have the same genetic information as southern mussels and they will be able to
detect the unique chemicals released by Asian shore crabs.
(D) There will be little to no change in the shell thickness of northern mussels because the
mussels already have thicker shells due to the presence of the unique chemicals released
by green crabs.
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1.2 C: Evidence for Evolution via Natural Selection Quiz
4.
Lactase is an enzyme needed to digest lactose, the sugar found in milk. Almost all humans carry
the gene to produce lactase. Until about 20,000 years ago, the lactase gene was turned off by
regulatory genes after infancy. Today, many people have the dominant allele (R) of a regulatory
gene, which keeps the lactase gene turned on in adulthood. The table below shows the allelic
frequencies for the regulatory gene in four countries.
In Africa, the R allele is not present in the Tutsi population, but 90% of the individuals have three
other mutations that keep the lactase gene functional in adulthood.
Which statement best supports the data shown?
(A) Over the past 20,000 years, the German and Tutsi populations had a selective advantage
favoring lactase expression in adults and Chinese populations had a selective advantage
favoring alleles that suppress lactase expression in adults.
(B) Over the past 20,000 years, there has been a strong selective pressure to be able to
digest lactose within the German and Tutsi populations, but this selective pressure was not
as strong in Spain and France, and is relatively nonexistent in China.
(C) Over the past 20,000 years, individuals in the Chinese population did not drink enough
milk to cause the mutations to the regulatory gene that allows for the production of lactase
into adulthood.
(D) Over the past 20,000 years, the German, French, Spanish, and Tutsi populations
developed lactose tolerance due to the occurrence of simultaneous random mutations in
most of the individuals in the population.
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1.2 C: Evidence for Evolution via Natural Selection Quiz
5.
Fire ants (Solenopsis invicta) were first introduced into the southern United States in the 1930s
and spread quickly throughout the southern states. At that time, nearly all fire ants were found in
colonies with a single queen, called monogyne colonies. In the 1970s, scientists discovered that
some colonies, called polygyne colonies, had multiple queens. Monogyne colonies produce
more offspring in areas with few colonies, but have a reduced chance of survival in areas with
many competing colonies. Polygyne colonies, on the other hand, have an increased rate of
survival in areas with competing colonies.
The ability to form polygyne colonies is due to a mutation in a single gene: Gp-9. There are two
versions of Gp-9, B and b, which produce different responses in ants. The chart below shows
how genotype affects behavior.
Which statement best predicts how the allele frequencies (B and b) of the Gp-9 gene have
changed among the growing fire ant population in the United States since the 1930s?
(A) Since queens with genotype bb are weak and usually die, the B allele will increase in
frequency compared to the weaker b allele due to natural selection.
(B) Since workers with genotype BB kill all invading queens, the B allele will increase in
frequency compared to the b allele.
(C) Because polygyne colonies have a greater survival rate in areas with multiple colonies
than monogyne colonies do, the Bb genotype is favored and the b allele will increase in
frequency.
(D) Because monogyne colonies produce more offspring than polygyne colonies do, the B
allele will increase in frequency as more BB queens are produced and establish more
colonies.
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