7.4 Population Genetics

The gene pool

A population is a group of interbreeding individuals; all their alleles together form the gene pool. A change in allele frequencies over time is microevolution — evolution at the population level.

Mechanisms of change

Allele frequencies change through: natural selection, mutation (new alleles), gene flow (alleles moving between populations via migration), genetic drift (random change, strongest in small populations — includes the bottleneck and founder effects), and nonrandom mating.

Key terms

Gene pool

All the alleles present in a population.

Microevolution

A change in allele frequencies within a population over time.

Genetic drift

Random change in allele frequencies, strongest in small populations.

Gene flow

Movement of alleles between populations through migration.

Bottleneck / founder effect

Drift from a sharp population crash (bottleneck) or a few founders starting a new population.

Try an AP-style question

A storm kills 90% of a beetle population at random, regardless of their traits. Allele frequencies in the survivors differ from before. What caused this change?

1. Genetic drift (a bottleneck effect)
2. Gene flow from another population
3. New mutations caused by the storm
4. Natural selection for storm resistance