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AP®BiologyCollege BoardExam QuestionsUnit 7: Natural SelectionPopulation Genetics

Population Genetics (College Board AP® Biology)

Exam Questions

5 mins5 questions
11 mark

In a large population of fruit flies, the frequency of an allele for eye color remains constant at 0.3 across many generations, despite no apparent selective advantage. Which of the following best explains this stability in allele frequency?

  • The population is experiencing natural selection for eye color.

  • Genetic drift is causing random fluctuations in allele frequency.

  • The population meets some of the assumptions of the Hardy-Weinberg model.

  • The population is experiencing gene flow from neighboring populations.

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2
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The ability to roll one’s tongue is under the control of a single gene. The gene has two alleles R and r. People who can roll their tongue can have the genotypes RR or Rr. People who cannot roll their tongue have the genotype rr. A survey showed that 12 % of the student population in a single school could not roll their tongues. A student used the Hardy-Weinberg equations below to calculate the number of heterozygous individuals in the school:

p + q = 1

p2 +2pq + q2 = 1

Which of the following represents the percentage of heterozygous individuals at the student’s school?

  • 88 %

  • 35 %

  • 65 %

  • 46 %

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31 mark

A population of lizards (Anolis sagrei) colonized a small Caribbean island. The lizards had originally been part of a larger population on another nearby island. A team of geneticists compared the diversity of scale color alleles of the recently founded population with those of the larger source population. The frequency of scale color alleles in both populations is shown in Figure 1 below.

Bar chart showing scale colour allele frequency for white, yellow, and green in source and founded populations. White allele is highest in founded.
Figure 1. Scale color allele frequency in the source population and the founded population.
Bar chart showing allele frequency by scale colour. White: 0.9 founded, 0.2 source; Yellow: 0.3 source, 0.1 founded; Green: 0.4 source, 0.05 founded.

Which of the following conclusions is best supported by the data?

  • Natural selection has favored white scales on the small island.

  • The founder effect is affecting the lizard population on the island.

  • Mutation has given rise to new scale color alleles in the founded population.

  • Gene flow between islands has maintained similar allele frequencies.

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41 mark

A population geneticist studied allele frequencies in a small, isolated population of butterflies over several generations. The frequency of a recessive allele for wing pattern was tracked, and the results are shown in Figure 1 below.

Line graph showing allele frequency on the y-axis against number of generations on the x-axis, fluctuating between 0.4 and 0.7 over 10 generations.
Figure 1. Allele frequency changes over several generations of butterflies.
Line graph showing allele frequency changes over 10 generations, with peaks at generations 2 and 9 and a dip around generation 6, ranging from 0.4 to 0.7.

Which of the following processes is most likely to be responsible for the observed pattern of allele frequency changes?

  • Natural selection against the recessive allele.

  • Genetic drift.

  • Gene flow from neighboring populations.

  • A consistent change in environmental conditions.

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51 mark

Researchers studying a population of seed-eating finches on Daphne Major island in the Galapagos measured the beak depths of all finches on the island in 1976, then again in 1978 after a severe drought. A result of the drought was an increase in the number of large, tough seeds and a decrease in the number of small, soft seeds on the island. The beak depth measurements and population size before and after the drought are shown in the table below.

Year

Mean beak depth (mm)

Population size

1976

9.42

751

1978

9.96

90

Which of the following best explains the change in mean beak depth from 1976 to 1978?

  • The drought caused mutations to occur in the finch DNA that specifically led to an increase in beak size.

  • Overall mutation rates increased due to environmental stress.

  • A bottleneck effect has caused a random shift in allele frequencies.

  • Natural selection has increased the frequency of advantageous alleles.

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