Diversity of Individuals and Evolution of Populations Chapter 23 Diversity of Individuals and Evolution of Populations 1

I. Evolution occurs with the gradual change in the allele frequency within a population over time a population of one species has a variety of individuals for any feature, there can be many phenotypes phenotypes are determined by alleles must examine change in allele frequency of a population over time

II. Examining population’s allele and genotype frequency to study evolution population - localized group of individuals of the same species species - a group of populations that can interbreed gene pool - all alleles for all genes present in a population genetic structure of a population - population frequency of alleles & genotypes

III. Hardy-Weiberg theorem for a non-evolving population - a look at population structure Assume a gene with 2 alleles: A and a allele frequency is: A (0.8 = 80%) and a (0.2 = 20%) chance of AA offspring = 0.8 x 0.8 = 0.64** chance of aa offspring = 0.2 x 0.2 = 0.04** chance of Aa offspring = (0.8 x 0.2) x 2 = 0.32 ** ** this would be expected genotype structure at equilibrium (Hardy-Weinberg equlibrium)

Assume a gene with 2 alleles: A and a frequency of allele #1 (eg. A = 0.8) = p frequency of allele #2 (eg. a = 0.2) = q chance of resulting in AA = p x p = p2 chance of resulting in aa = q x q = q2 chance of resulting in Aa = 2 (p x q) = 2 p q p2 + 2 p q + q2 = 1 allows us to calculate population structure

IV. Evolution is - a generation-to-generation change in a population’s frequency of alleles and genotypes change in the Hardy-Weinberg frequency over time is a sign that some alleles can result in a phenotype which gives a “selective” advantage over other alleles for Hardy-Weinberg equilibrium to be maintained: large population size must exist no gene flow from other populations can occur no net mutations can occur random mating must be happening no natural selection can be occurring

V. Deviations from Hardy-Weinberg can result from: genetic drift (population size) gene flow mutation results in new alleles non-random mating (assortive mating, inbreeding) natural selection (differential success of offspring)

VI. Natural selection is dependent upon variation - alleles that give rise to a variety of phenotypes most phenotypes are the result of multiple genes polymorphism - variation of a certain item for discussion sources of polymorphism: genetic mutation - results in new and different alleles recombination - results new combinations of alleles

VII. Fitness - the relative contribution of an individual to the population gene pool Think about what is meant by the following: gene, allele, genotype, phenotype species population natural selection allele and genotype structure of a population evolution