AP Biology: Allele Frequency Change Practice Questions
Practice allele frequency change with original AP Biology multiple-choice questions. Each item connects population data, evolutionary mechanisms, and Hardy-Weinberg assumptions with clear explanations.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
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1. In a population with two alleles, B and b, the frequency of B changes from 0.62 to 0.74 over several generations. What does this change show?
Explanation. Evolution can be defined as a change in allele frequencies in a population over generations. A shift from 0.62 to 0.74 for allele B shows evolutionary change at that locus.
2. A pesticide is applied to a crop field. Before spraying, resistance allele R has a frequency of 0.04. After several generations, R has a frequency of 0.48 because resistant insects survive and reproduce more. Which mechanism best explains the change?
Explanation. The pesticide acts as a selective pressure. Insects carrying the resistance allele have higher survival and reproductive success, so the allele becomes more common.
3. A forest fire randomly kills most individuals in a small lizard population. The survivors happen to carry fewer copies of one allele than the original population. Which mechanism most directly changed allele frequencies?
Explanation. A bottleneck is a random reduction in population size that can change allele frequencies by chance. This is a form of genetic drift, especially important in small populations.
4. A population of wildflowers receives pollen from a nearby population where allele A is much more common. If the pollen produces offspring, what is the most likely effect?
Explanation. Gene flow is the movement of alleles between populations. If incoming pollen contributes to the next generation, it can shift allele frequencies in the receiving population.
5. Which event can introduce a completely new allele into a population?
Explanation. Mutation is the ultimate source of new alleles. Selection, drift, and gene flow can change frequencies of alleles, but mutation can create a new allele.
6. In a diploid population, genotype counts are AA = 50, Aa = 30, and aa = 20. What is the frequency of allele A?
Explanation. There are 100 individuals and 200 total allele copies. A copies = 2(50) + 30 = 130, so the frequency of A is 130/200 = 0.65.
7. A rare allele becomes common in a small isolated population even though it does not improve survival or reproduction. Which explanation is most consistent with the data?
Explanation. In small populations, random sampling effects can make neutral alleles increase or decrease in frequency. This is genetic drift.
8. A bird population is in Hardy-Weinberg equilibrium for a two-allele locus. Which statement best describes allele frequencies across generations?
Explanation. Hardy-Weinberg equilibrium predicts stable allele and genotype frequencies when assumptions such as random mating, no selection, no mutation, no migration, and large population size are met.
9. A population has allele frequencies p = 0.8 and q = 0.2. After migration from another population, q increases to 0.35. Which Hardy-Weinberg assumption has been violated?
Explanation. Migration can move alleles between populations. A change in q caused by incoming individuals violates the no-migration assumption.
10. Which scenario is most likely to decrease genetic variation within a population?
Explanation. A bottleneck can remove alleles by chance and reduce variation. Gene flow and mutation often add variation, while random mating alone does not usually remove alleles.
11. A student says, "Natural selection changes allele frequencies because individuals decide to adapt." Which correction is most accurate?
Explanation. Natural selection acts on heritable variation already present or introduced by mutation. Individuals do not decide to change their inherited alleles in response to need.
12. Two populations of the same species are separated by a mountain range. Over time, each population experiences different selection pressures and little gene flow. What is the most likely long-term result?
Explanation. Different selection pressures and limited gene flow can cause populations to accumulate different allele frequencies over time.
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FAQ
What counts as allele frequency change in AP Biology?
Any measurable shift in how common an allele is in a population across generations counts as allele frequency change and can indicate evolution at that locus.
Which mechanisms change allele frequencies?
Natural selection, genetic drift, gene flow, mutation, and nonrandom mating can all affect genotype or allele frequencies, although mutation is the original source of new alleles.
How do I avoid mistakes on allele frequency questions?
Keep the level of analysis clear: individuals have genotypes, populations have allele frequencies, and evolution is measured across generations.