1. Evolution of Populations Population genetics is the study of how gene frequencies in a population change over time. – The physical representation of genes (phenotypes) eventually gave rise to the Modern Synthesis which is a comprehensive theory of how evolution effected the change. population - a local group capable of interbreeding gene pool - total aggregate of genes

2. Hardy-Weinberg The Hardy-Weinberg theorem (p 2 +2pq+q 2 = 1) describes gene frequencies in a stable population that are well adapted to the environment. It assumes the following: – Extremely large populations – No gene flow between populations – Random mating – No natural selection As you can see the chance for a these conditions leading to a stable population is entirely improbable. Any departure in these conditions leads to evolution. Why it doesn’t work

3. Agents of evolution Mutation – point - changes in a single base sickle cell disease - heterozygous individual has an advantage in Malaria prone areas – duplication although most duplications are harmful some duplications through transposable elements have no adverse effects on an organism. over time the duplications lead to an expanded genome – mutation rate - organisms with a high mutation rate (viruses and bacteria) evolve faster Seen in drug resistance

4. Agents of evolution Sexual recombination – this single event is more important to adaptation leading to evolution than any other single process – makes natural selection possible Or FON

5. Agents of evolution Genetic Drift - deviations from expected (Hardy-Weinberg) frequencies – bottle-neck effect caused by a disaster suddenly altering the environmental pressures causing the genes of a few survivors to dominate – founder effect when a few individuals move and start a new population allowing their genes to dominate – gene flow changes to a gene pool as individuals move out and into a breeding population tends to reduce differences between populations

6. Stabilization of a gene pool Directional selection – selection toward a phenotype that is best adapted to the environment – most common type of selection Disruptive selection – occurs when environmental factors favor individuals on both extremes of the phenotypic range – often to facilitate different food sources

7. Stabilization of a gene pool Stabilizing selection – selects against the extremes of phenotypes – humans Balancing Selection – occurs when nature allows 2 distinctly different polymorphisms to exist in relatively equal frequencies (balanced polymorphism) – leads to heterozygous advantage and frequency dependent selection heterozygous advantage - heterozygous individuals exhibit less genetic disorders frequency dependent selection - frequency of the dominant phenotype becomes less fit over time (prey species)