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Group Notes23 - Evolved 20 Original 80 20 80 W 20(a...

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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:
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-Mutations in noncoding regions of DNA are often harmless -Mutations in a gene might not affect protein production because of redundancy in the genetic code
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