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Hardy-Weinberg equilibrium describes populations that are not evolving. Genotype frequencies stay the same if five conditions are met. –very large population: no genetic drift –no emigration or immigration: no gene flow –no mutations: no new alleles added to gene pool –random mating: no sexual selection –no natural selection: all traits aid equally in survival
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KEY CONCEPT Hardy-Weinberg equilibrium provides a framework for understanding how populations evolve.
Hardy-Weinberg equilibrium describes populations that are not evolving. • Biologists use models to study populations.• Hardy-Weinberg equilibrium is a type of model.
Hardy-Weinberg equilibrium describes populations that are not evolving. • Genotype frequencies stay the same if five conditions are
met.– very large population: no genetic drift – no emigration or immigration: no gene flow – no mutations: no new alleles added to gene pool– random mating:
no sexual selection– no natural selection:
all traits aid equallyin survival
Hardy-Weinberg equilibrium describes populations that are not evolving. • Real populations rarely meet all five conditions.
– Real population data iscompared to a model.
– Models are used tostudy how populationsevolve.
Analyzing Gene Pools
Gene pools are all alleles in a population (remember 1 individual has 2 alleles for each trait; EX: RR, Rr, or rr)• p = frequency of dominant alleles =
#R/total alleles• q = frequency of recessive alleles =
#r/total allelesp + q = 1
We can use the Hardy-Weinberg formula to calculate genotype frequencies:
p2 + 2pq + q2 = 1• p2 = RR• 2pq = Rr• q2 = rr
Practicing H-W Equation• 200 flower; red is dominant to white• 143 flowers are red; 57 flowers are white• Red Genotypes = RR or Rr• White Genotype = rr• Total alleles = 400• p2 + 2pq + q2 = 1 or RR + Rr + rR + rr = 1• q2(rr) = 57/200 = 0.285• q = √0.285 = 0.534 • p + q = 1 therefore p = 1 – q = 1 – 0.534 = 0.466• p2(RR) = (0.466)2 = 0.217• (0.217) + 2(0.466)(0.534) + (0.285) = 1• 0.217 + 0.498 + 0.285 = 1• RR = 21.7%; Rr = 49.8%; rr = 28.5% therefore red =
71.5% & white = 28.5%