What is a population? All the individuals of a species that live together in one place at one time.

Populations: How they evolve Allele Frequencies a. Hardy-Weinberg: frequencies of alleles in a population do not change unless evolutionary forces act on the population ex: a dominant allele that is lethal will not become more common just because its dominant, in fact it will become rare as they die. b. This principal holds true as long as the members do not mate with relatives and there are no evolutionary forces acting on the population. c. Evolutionary forces: cause the ratios of the genotypes in a population to differ from those predicted from Hardy- Weinberg Hardy-Weinberg Equation: p2+2pq+q2 (B2 +2Bb + b2 )

Evolutionary Forces Five Evolutionary forces 1. Mutations a. Slow, changes frequencies over a long period of time b. Genes mutate 1 to 10 for every 100,000 cell divisions c. Not all mutations change a phenotype, some codons code for the same amino acid so would not change the protein resulting in no effect. 2. Gene Flow a. Migration: the movement of individuals from one population to another. b. Movement of alleles into or out of the population

Evolutionary Forces 3. Nonrandom Mating: a. Inbreeding- changes the number of homozygous individuals b. Choose their mates based on certain traits Male widowbirds have evolved long tails because females widowbirds prefer to mate with males that have long tails over males with short tails.

a. Change in allele frequency caused by a chance event. Ex; Fire 4. Genetic Drift a. Change in allele frequency caused by a chance event. Ex; Fire b. Small population that are isolated from each other can differ greatly as a result of genetic drift. c. Cheetahs :Example of Genetic Drift Cheetahs exhibit much lower levels of variation than other mammals. In most species, related individuals share about 80 percent of the same genes. With cheetahs, this figure rises to approximately 99 percent. The genetic inbreeding in cheetahs has led to low survivorship (a large number of animals dying), poor sperm quality, and greater susceptibility to disease. Inbred animals suffer from a lack of genetic diversity.

5. Natural Selection