Evolution and Classification
Evolution and Classification tests natural selection, evidence for evolution, speciation and Hardy–Weinberg calculations. Classification questions test taxonomic hierarchy, binomial nomenclature, phylogeny and the three-domain system.
Core rules
- Natural selection requires heritable variation, differential survival or reproduction, and a change in allele frequency over generations.
- Evidence includes fossils, comparative anatomy (homologous structures), embryology, molecular sequences and biogeography.
- Speciation occurs when gene flow is interrupted; allopatric speciation involves geographic isolation, sympatric speciation does not.
- The taxonomic hierarchy is domain, kingdom, phylum, class, order, family, genus, species; binomial names are italicised or underlined, with the genus capitalised.
- Phylogenetic trees show common ancestry; homologous structures reflect shared ancestry, analogous structures reflect convergent evolution.
Worked example
In a population at Hardy–Weinberg equilibrium, 16% show the recessive phenotype. q² = 0.16, so q = 0.40 and p = 0.60. Heterozygote frequency = 2pq = 2 × 0.60 × 0.40 = 0.48, or 48%. Reasoning: the recessive phenotype frequency equals q² only if the population is large, randomly mating and free of selection, mutation and migration.
Traps
- Acquired characteristics are not inherited; only genetic changes evolve.
- Analogous structures do not indicate close relatedness.
- “Domain” is above kingdom; “species” is the basic unit.