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Population Genetics Population “Localized group of individuals…capable of interbreeding and producing fertile offspring”

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

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Population Genetics Population “Localized group of individuals…capable of interbreeding and producing fertile offspring”

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  1. 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

  2. Fig. 23.6

  3. 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?

  4. 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

  5. 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

  6. Fig. 23.8

  7. 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

  8. 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

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