Which best describes the effect on the survivor population?

Answer: Reduced genetic variation due to non-representative sampling A bottleneck dramatically reduces population size, and the surviving alleles are essentially a random subset of the original. The result is reduced genetic variation and altered allele frequencies regardless of fitness.

Two individuals colonize an island. Which best describes the genetic outcome on the island?

Answer: Founder effect: allele frequencies in colony differ from mainland by chance The founder effect describes how a small group establishing a new population carries only a fraction of the source population's variation, leading to allele frequency differences and reduced diversity by chance.

The data are best explained by:

Answer: Directional selection favoring R in the presence of pesticide. A steady, large rise in R allele frequency under a consistent selection pressure (pesticide) is classic directional selection.

AP Biology · Topic 7.4

Population Genetics Practice

Part of Natural Selection.(EVO-1.D)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$A natural disaster sharply reduces a population's size; only a fraction of individuals survive to reproduce.$
$Which best describes the effect on the survivor population?$
- A
  $Higher mutation rate in survivors$
- B
  $Reduced genetic variation due to non-representative sampling$
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- C
  $No change in allele frequencies because selection was not the cause$
- D
  $Increased heterozygosity from inbreeding$
Why
$A bottleneck dramatically reduces population size, and the surviving alleles are essentially a random subset of the original. The result is reduced genetic variation and altered allele frequencies regardless of fitness.$
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Sample 2difficulty 1/5
$Two individuals leave a large mainland population and establish a small colony on a previously uninhabited island.$
$Two individuals colonize an island. Which best describes the genetic outcome on the island?$
- A
  $Migration: continuous gene flow homogenizes populations$
- B
  $Sexual selection: only fit individuals reproduce on the island$
- C
  $Bottleneck: same population reduced by environmental disaster$
- D
  $Founder effect: allele frequencies in colony differ from mainland by chance$
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Why
$The founder effect describes how a small group establishing a new population carries only a fraction of the source population's variation, leading to allele frequency differences and reduced diversity by chance.$
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Sample 3difficulty 2/5
$A population of insects exposed to pesticide was sampled annually. The frequency of the resistance allele R was tracked over 10 generations.$
$The data are best explained by:$
- A
  $Random mutation creating R individuals every generation.$
- B
  $Genetic drift in a large stable population.$
- C
  $Stabilizing selection maintaining the average phenotype.$
- D
  $Directional selection favoring R in the presence of pesticide.$
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Why
$A steady, large rise in R allele frequency under a consistent selection pressure (pesticide) is classic directional selection.$
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Sample 4difficulty 2/5
$Frequency of an antibiotic-resistance allele in a bacterial population is monitored before and after antibiotic introduction.$
$What best explains the rapid rise in resistance allele frequency after antibiotic introduction?$
- A
  $Genetic drift unrelated to the antibiotic$
- B
  $Strong directional selection favoring pre-existing resistant variants$
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- C
  $Hardy-Weinberg equilibrium being maintained$
- D
  $Bacteria mutated specifically in response to the antibiotic to acquire resistance$
Why
$Pre-existing resistance alleles, present at low frequency, were strongly favored by selection once antibiotics were introduced. Mutations are random with respect to need; selection acts on standing variation.$
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Sample 5difficulty 2/5
$Genetic drift refers to$
- A
  $Migration-driven changes in allele frequencies, especially significant in isolated populations$
- B
  $Random changes in allele frequencies, especially significant in small populations$
  check_circle
- C
  $Adaptive changes in allele frequencies, especially significant in stable populations$
- D
  $Directional changes in allele frequencies, especially significant in large populations$
Why
$Drift is sampling error in transmission of alleles between generations; smaller populations are more affected.$
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