AP Biology · Summary

Unit 7 summary

1. Natural selection needs heritable variation and unequal survival or reproduction; individuals are selected, but populations evolve.
2. Fitness is the number of offspring that survive and reproduce, compared with others in the population, not lifespan or strength.
3. Count gene copies: frequency of A = (2 x AA + Aa) / (2 x total). For two alleles, p + q = 1 and p² + 2pq + q² = 1.
4. Hardy-Weinberg is the no-evolution baseline: a large population, random mating, no mutation, no gene flow and no selection. A mismatch means at least one condition is not being met.
5. Drift is chance change, strongest in small populations; gene flow makes populations more alike; selection favors alleles that help in the current environment.
6. On a tree, relatedness comes from the most recent shared node; fewer sequence differences mean a more recent common ancestor.
7. New species form when reproductive isolation arises, often after a barrier stops gene flow; small populations with little genetic variation are at higher risk of extinction.