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%