Population Genetics Population “Localized group of individuals…capable of interbreeding and producing fertile offspring” Isolated from other populations of the same species to some extent

Fig. 23.6

Population Genetics Population Gene pool – All genes in a population at a given time Fixed allele – Only one allele at a particular locus in a population In a population, each allele has a frequency Ex: Population of wildflowers with two alleles (CR, CW) at locus for flower pigment Homozygous CR – Red flowers Homozygous CW – White flowers Heterozygous – Pink flowers Population – 320 plants with red flowers, 160 with pink flowers, 20 with white flowers Question – Allele frequencies for CR and CW?

Population Genetics Hardy-Weinberg Theorem Describes distribution of alleles and traits in populations that are not evolving Population in genetic equilibrium Frequencies of alleles and genotypes in a gene pool remain constant over generations Mendelian inheritance preserves variation

Population Genetics Hardy-Weinberg Theorem Permits calculation of allele frequencies from genotype frequencies and vice-versa Frequency of any allele can be described as a number between 0 and 1 Ex: Population of wildflowers (alleles CR, CW) Sum of allele frequencies = 1 Frequencies of alleles = p, q p + q = 1 (p + q)2 = p2 + 2pq + q2 = 1 p2 – Freq. of CRCR individuals in population 2pq – Freq. of CRCW individuals in population q2 – Freq. of CWCW individuals in population

Fig. 23.8

Population Genetics Hardy-Weinberg Theorem Proportion of alleles in population doesn’t change over successive generations, provided five conditions are met No net mutations Random mating Mates not selected based on genotype No natural selection Favors certain geno- and phenotypes, leading to changes in allele frequencies Extremely large population size Random fluctuation (genetic drift) more prevalent and influential in small populations No gene flow

Microevolution Evolution occurs when populations don’t meet all the H-W assumptions Process by which a population’s genetic structure changes = microevolution Changes in allele frequencies result from five evolutionary processes Mutation Nonrandom mating Natural selection Genetic drift Gene flow