HARDY-WEINBERG & EVOLUTION

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Presentation transcript:

HARDY-WEINBERG & EVOLUTION ALLELE FREQUENCY HARDY-WEINBERG & EVOLUTION

HARDY - WEINBERG A population that is not changing genetically is said to be at Hardy–Weinberg equilibrium The assumptions that underlie the Hardy–Weinberg equilibrium are population is large mating is random There is no migration (no immigration or emigration) There is no mutation of the alleles natural selection is not acting on the population. (all genotypes have an equal chance of surviving and reproducing)

HARDY-WEINBERG & EVOLUTION Biologists can determine whether an agent of evolution is acting on a population by comparing the population’s genotype frequencies with Hardy–Weinberg equilibrium frequencies. If there is no change in frequencies, there is no evolution Conversely, if there have been changes in the frequencies, then evolution has occurred. Evolution is change of allelic frequencies

HARDY – WEINBERG formula Two equations given on the formula sheet p + q = 1 A + a = 1, where A and a equal gene percentages All dominant alleles + all recessive alleles = all of the alleles for a particular gene in a population Allele frequencies p2 + 2pq + q2 = 1 AA + 2Aa + aa = 1 For a particular gene, all homozygous dominant individuals + all heterozygous individuals + all homozygous recess individuals = all of the individuals in the population Genotype frequencies

HARDY-WEINBERG PROBLEM Given: In a population of 100 individuals (200 alleles), sixteen exhibit a recessive trait. Problem: Find the allele frequencies for A and a. Find the genotypic frequencies of AA, Aa, and aa. Allele frequency: p + q = 1 or A + a = 1 16% = aa & 84% = AA +Aa aa = qq or q2 = .16 or q = .4 1 - q = p 1 - .4 = .6 or A = .6 and a = .4

HARDY - WEINBERG PROBLEM Phenotypic frequencies If: p = .6 and q = .4, then p2 = (.6)(.6) = .36 q2 = (.4)(.4) = .16 2pq = 2(.6)(.4) = .48 Therefore, in the population: Homozygous dominant = 36/100 or 36% Heterozygous dominant = 48/100 or 48% Recessive = 16/100 or 16%

ANOTHER PROBLEM Fraggles are mythical, mouselike creatures that live beneath flower gardens. Of the 100 fraggles in a population, 91 have green hair(F) and 9 have grey hair(f). Assuming genetic equilibrium: What are the gene frequencies of F and f? What are the genotypic frequencies?

ANSWERS TO PROBLEM Gene frequencies: Genotypic frequencies F = 0.7 and f = 0.3 Genotypic frequencies FF = 49% or 0.49 Ff = 42% or 0.42 f f = 9% or .09