Evolution and Biodiversity
What this domain tests
Evolution and Biodiversity tests the mechanisms that change allele frequencies, the evidence for common descent, and how biodiversity is organized. Expect Hardy–Weinberg calculations, phylogenetic interpretation, and questions that separate selection from drift.
Core rules and concepts
- Evolution is change in allele frequencies in a population, not change in an individual.
- Natural selection requires heritable variation and differential reproductive success.
- Genetic drift is random, strongest in small populations; gene flow moves alleles between populations.
- Hardy–Weinberg: p + q = 1; p² + 2pq + q² = 1 for two alleles.
- Speciation can be allopatric via geographic isolation or sympatric via polyploidy or behavioral isolation.
- Phylogenies show common ancestry; they do not imply that extant species are more evolved.
Worked example
A recessive disease affects 4% of a population, so q² = 0.04. Then q = 0.2, p = 0.8. Carrier frequency 2pq = 2(0.8)(0.2) = 0.32, or 32%. Reasoning: the Hardy–Weinberg equation converts phenotype frequency to allele frequency only if the population meets assumptions; if selection against the disease is strong, the estimate is approximate.
Traps that cost marks
Do not say individuals evolve to adapt. Do not confuse genetic drift with natural selection: drift is random with respect to fitness. Do not assume a trait is adaptive just because it is common. Do not interpret a phylogenetic tree as a ladder. Do not forget that mutation creates new alleles but is slow compared with selection or drift in changing frequencies.