I. Population Evolution A. Macro 1. large scale changes 2. long periods of time B. Micro 1. changes within populations (interbreeders in a given area) 2. change in allele frequencies alleles: alternative forms of a gene 3. driven primarily by natural selection real essence of Darwin’s ideas of evolution

C. Why do original genotype proportions often remain constant? 1. allele frequencies (proportions of alleles of a given gene) 2. dominant alleles do not replace recessives (in randomly mating populations) 3. Hardy-Weinberg equilibrium indicates population is not evolving 4. Hardy-Weinberg theorem (p + q)2 = p2 + 2pq + q2 p = dominant allele q = recessive allele If only 2 alleles, then p + q = 1

p2 + 2pq + q2 = 1 p = 1 - 0.4 q2 = 0.16 p = 0.6 q = 0.4 p2 = 0.36 p + 0.4 = 1 2pq = 2 x 0.6 x 0.4 = 0.48 0.36 + 0.48 + 0.16 = 1

p2 + 2pq + q2 = 1 p = 1 - 0.2 q2 = 0.04 p = 0.8 q = 0.2 p2 = 0.64 p + 0.2 = 1 2pq = 2 x 0.8 x 0.2 = 0.32 0.64 + 0.32 + 0.04 = 1

5. Hardy Weinberg theorem is based on assumptions: a. a large (almost infinite) population size b. random mating c. no natural selection d. no new alleles introduced - migration, mutation, etc. Evolution is normally so slow as to give the appearance of Hardy-Weinberg equilibrium

II. Changes in Allele Frequencies (usually ratio of homozygotes to heterozygotes) Factors that can cause variation in Hardy-Weinberg: A. Mutation 1. maybe replication error 2. change in DNA sequence a. harmful b. benign c. beneficial (rare) 3. mutation rate probably too low to change most allele frequencies

B. Migration 1. individual from one population moves to another population 2. depends on the ability of the immigrant to survive and breed 3. includes transport of gametes and/or zygotes 4. gene flow - tends to reduce the number of differences among populations - free movement of humans

C. Genetic drift 1. often involves loss of alleles 2. maybe the result of drastic events 3. also can come from isolation 4. founder effect a. one or more individuals carrying certain alleles b. certain alleles may become more common as those individuals interbreed c. good explanation for Darwin’s finches

5. bottleneck effect a. event drastically reduces population size b. surviving small population will have less genetic variability (fewer alleles)

D. Nonrandom mating - inbreeding increases the number of homozygotes in a population ( higher than if in Hardy-Weinberg equilibrium) E. Selection 1. survival (reproduction) of the fittest 2. artificial - animal breeding 3. natural - by environment

Selection

Selection

Selection Sickle-cell trait represents which type of selection?