AP Biology 7.4: Population Genetics
Practise AP Biology 7.4 questions by analyzing random evolutionary processes, gene flow and allele-frequency changes in populations over time.
- Syllabus
- Effective Fall 2025
- Course
- AP Biology
Exam points
- distinguish mutation, genetic drift, bottleneck effect, founder effect and migration-driven gene flow
- predict how random processes, selection and population connectivity change allele frequencies and genetic diversity
- use allele-frequency, phenotype, sequence and graph data as evidence that a population has evolved
- evaluate genetic rescue and habitat-connectivity strategies for small isolated populations
Covered syllabus points
7.4 Population Genetics question 1
Questions 40-44 Sea otters are native to the western coast of North America. Between 1750 and 1850, hunting had reduced the population from hundreds of thousands to only one thousand individuals. In the early 1900s, a small population of sea otters was discovered in Elkhorn Slough, an estuary in central California near a large human population center. The otters were then protected by the international fur seal treaty, which banned sea otter hunting. The sea otter population has rebounded to nearly three thousand individuals today. Otters live in kelp forests and eelgrass beds and feed on crabs and shellfish (Figure 1). Most herbivores in the habitat eat algae that grows on the eelgrass and not the eelgrass itself. If there is too much algae, the eelgrass does not receive enough light for photosynthesis. As the otter population has increased, the eelgrass habitat has increased.
Figure 1. Partial food chain in eelgrass habitats
Recently, however, scientists have noticed the presence of two nonnative, predatory invertebrate species that may be colonizing the Elkhorn Slough, which would have been too cold for them three decades ago. Scientists have also observed that otters in the area are experiencing increased mortality because of an increase in harmful algal blooms, which occur as a result of nutrient pollution. The harmful algae are ingested by shellfish, which the otters eat.
Which of the following best describes what happened to the otter population between 1750 and 1850 ?
A
The population decreased in size as a result of a loss of genetic diversity.
B
The population decreased in size as a result of habitat loss.
C
The population lost genetic diversity as a result of a bottleneck effect.
D
The population lost genetic diversity as a result of the founder effect.
7.4 Population Genetics question 2
Scientists have found that the existing populations of a certain species of amphibian are small in number, lacking in genetic diversity, and separated from each other by wide areas of dry land. Which of the following human actions is most likely to improve the long-term survival of the amphibians?
A
Cloning the largest individuals to counteract the effects of aggressive predation
B
Reducing the population size by one-fifth to decrease competition for limited resources
C
Constructing a dam and irrigation system to control flooding
D
Building ponds in the areas of dry land to promote interbreeding between the separated populations
7.4 Population Genetics question 3
Twenty million years ago the Caribbean Sea and Pacific Ocean were connected, and water
flowed freely between the two bodies of water. Many of the same marine species were found
in both areas. Over millions of years, the land referred to as the Isthmus of Panama formed,
eventually closing off the connection between the Caribbean Sea and Pacific Ocean and creating
two separate bodies of water. The ecology of these two marine habitats was dramatically altered
by this land formation. The warmer Caribbean water could no longer flow west, so the Pacific
water cooled and became more nutrient-rich, while the Caribbean water became warmer.
Describe the genetic evidence that evolution is occurring in a population.
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