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Unformatted text preview: Alleles in the population Frequencies of alleles p = frequency of Gametes produced C R allele = 0.8 Each sperm: Each egg: q = frequency of 20% chance C W allele = 0.2 80% chance 20% chance 80% chance 20% chance Frequency of individuals Original population Phenotypes (fur color) Original population Evolved population (c) Stabilizing selection (b) Disruptive selection (a) Directional selection The Evolution of Populations: Chapter 23 • One misconception is that organisms evolve, in the Darwinian sense, during their lifetimes • Natural selection acts on individuals, but only populations evolve • Microevolution is defined as the change in allele frequencies in a populations over generations • Variation in individual genotype leads to variation in individual pheontype • Not all phenotypic variation is heritable • Natural selection can only act on variation with a genetic component. • Both discrete and quantitative characters contribute to variation within a population • Discrete characters can be classified on an either-or basis (purple flowers or white flowers) • Quantitative characters may vary along a continuum within a population(body length) • Population geneticists measure polymorphisms in a population by determining the amount of heterozygosity at the gene and molecular levels • Average heterozygosity measures the average percent of loci that are heterozygous in a population. • Nucleotide variability is measured by comparing the DNA sequences of pairs of individuals • Most species exhibit geographic variation , differences between gene pools of separate populations or population subgroups • Mutations are changes in the nucleotide sequence of DNA • Mutations cause new genes and alleles to arise • Only mutations in cells that produce gametes can be passed to offspring • A point mutation is a change in one base in a gene • The effects of point mutations can vary:-Mutations in noncoding regions of DNA are often harmless-Mutations in a gene might not affect protein production because of redundancy...
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