Origin and Evolution of Life
What the exam tests
Origin and evolution of life includes chemical evolution, evidence for evolution, natural selection, Hardy-Weinberg equilibrium, genetic drift, speciation, and human evolution.
Core rules
- Oparin and Haldane proposed chemical evolution; Miller and Urey produced amino acids from simple gases. The RNA world hypothesis suggests RNA preceded DNA and proteins.
- Evidence includes fossils, homologous and analogous organs, vestigial organs, embryology, and molecular similarities.
- Darwin's natural selection requires variation, heritability, and differential reproductive success. Fitness is reproductive success, not strength.
- Hardy-Weinberg: p + q = 1 and p^2 + 2pq + q^2 = 1 for a population not evolving. Genetic drift, gene flow, mutation, and selection change allele frequencies.
- Speciation can be allopatric or sympatric; reproductive isolation is key.
Worked example
A recessive genetic disorder affects 4% of a population (q^2 = 0.04). Then q = 0.2 and p = 0.8. Carrier frequency = 2pq = 2 × 0.8 × 0.2 = 0.32, or 32%. Reasoning: the Hardy-Weinberg equation separates genotype frequencies, so the square root of the affected frequency gives the recessive allele frequency.
Traps
Do not confuse homologous (same origin, different function) with analogous (different origin, same function) structures. Lamarck proposed inheritance of acquired characteristics; Darwin proposed natural selection. In Hardy-Weinberg, q^2 is the affected genotype frequency, not the allele frequency. Genetic drift is random, not selection.