Evolution
What this domain tests
Evolution tests the evidence for common descent, mechanisms of evolutionary change, population genetics, speciation, and phylogeny. Expect calculations with allele frequencies and interpretation of selection data.
Core rules and concepts
- Natural selection acts on phenotypic variation and requires heritability and differential reproductive success. It changes allele frequencies within populations; individuals do not evolve.
- Hardy–Weinberg equilibrium assumes no mutation, no migration, no selection, random mating, and a large population. Deviations suggest evolution is occurring.
- Genetic drift is random allele-frequency change, strongest in small populations. Gene flow moves alleles between populations. Mutation creates new alleles.
- Speciation can be allopatric, with geographic isolation, or sympatric, without it. Reproductive isolation prevents gene flow between species.
Worked example
A recessive disease affects 1 in 10,000 people. Under Hardy–Weinberg, q² = 0.0001, so q = 0.01. Then p = 1 − q = 0.99. Carrier frequency = 2pq = 2 × 0.99 × 0.01 = 0.0198, about 2%. Reasoning: the disease incidence gives the frequency of homozygous recessive genotypes; taking the square root gives q, and 2pq estimates heterozygotes.
Traps
Do not say an individual “evolves” during its lifetime. Do not assume the dominant allele is the most common. Check Hardy–Weinberg assumptions before applying the equations. Distinguish homologous structures, inherited from a common ancestor, from analogous structures produced by convergence.