individuals are resistant to HIV 1 infection Heterozygotes are susceptible to

Individuals are resistant to hiv 1 infection

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individuals are resistant to HIV-1 infection Heterozygotes are susceptible to infection but progress more slowly to AIDS Since this imparts resistance to HIV important questions to consider: Which human populations carry this allele? How common is it?
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CCR5 allele frequencies § Genotypes determined by direct DNA analysis using PCR § Allele frequency in a population can be determined by genotype counting § Sampling in the next generation can tell us if these alleles/genotypes are at HW equilibrium, and what factors are important in changing these frequencies if not q 2 = 0.11 2 = 0.01 p 2 = 0.89 2 = 0.792 2pq = 2x0.89x0.11 = 0.2
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Hardy–Weinberg’s unrealistic assumptions Hardy–Weinberg model assumes: § Random mating occurs § Equal rate of survival and reproduction ( no selection ) § No migration into or out of population § Infinitely large population § No new alleles arise or created by mutation In reality, all these things are very important and affect populations Evolutionary impact on a population can be quantified by determining the change in allele frequencies
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Random and non-random mating § Random mating means that individuals do not choose their mates on the basis of a particular heritable character § Nonrandom mating: § Positive assortative mating : Bias toward phenotypically similar mates § Negative assortative mating : Bias toward phenotypically different mates § Inbreeding : Bias toward mating with relatives
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Self-fertilization and inbreeding For a given allele: § Inbreeding increases proportion of homozygotes in population § Completely inbred population theoretically will consist only of homozygotes § Genotype frequencies change, but allele frequencies do not p=0.5, q=0.5 p=0.5, q=0.5 p=0.5, q=0.5
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Natural selection Natural selection favors the reproductive success of some members of a population over others Individuals with a favored phenotype survive to reproductive age at higher rates and/or reproduce at higher rates as a result of the favored phenotype: differential reproductive fitness Certain alleles will be passed to the next generation more often than others, changing allele frequencies in the population over time
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Differential Reproduction and Relative Fitness § If genotypes have unequal fitness, then allele frequencies will change over time ( natural selection) § Relative Fitness ( w ) is the survival and/or reproductive rate of a genotype relative to the maximum survival rate of other genotypes in the population. A measure of the intensity of natural selection § Hardy-Weinberg assumes equal fitness: Genotype AA Aa aa Fitness 1 1 1
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Relative fitness and selection coefficient § Individuals that reproduce less successfully than the most favored genotype have decreased relative fitness § The proportion of this decrease is called the selection coefficient ( s ) Relative Fitness (s), w = 1 – s Example: an organism without a trait reproduces 60% as well as organism with the trait, its relative fitness w is 0.6, selection coefficient s is 0.4
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Directional Natural Selection §
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  • Spring '08
  • Pratt

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