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I. Population Genetics A. 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 I. Population Genetics A. 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? I. Population Genetics B. 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 I. Population Genetics B. 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 I. Population Genetics B. Hardy-Weinberg Theorem • Proportion of alleles in population doesn’t change over successive generations, provided five conditions are met 1) 2) No net mutations Random mating • Mates not selected based on genotype 3) No natural selection • Favors certain geno- and phenotypes, leading to changes in allele frequencies 4) Extremely large population size • Random fluctuation (genetic drift) more prevalent and influential in small populations 5) No gene flow II. 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 1) 2) 3) 4) 5) Mutation Nonrandom mating Natural selection Genetic drift Gene flow