Hardy-Weinberg Equilibrium

1. Hardy-Weinberg Equilibrium Honors Biology

2. Is evolution occurring right now? • How might a scientist tell if evolution is occurring within a population?

3. Hardy-Weinberg Equilibrium • Biologists use models to study populations • Hardy-Weinberg equilibrium is a type of model • Provides a framework for understanding how populations evolve

4. Hardy-Weinberg Equilibrium Conditions • Genotype frequencies stay the same (no microevolution) if all 5 conditions are met: • Very large population size • Isolation from other populations • No Mutations • Random Mating • No natural selection

5. The Hardy-Weinberg Equation • Uses frequencies of alleles in a population’s gene pool to determine if (micro)evolution is occurring • If allele frequencies change over time, the population is evolving • If allele frequencies are stable, the population is at equilibrium

6. Hardy-Weinberg Equation • p + q = 1 • p = frequency of dominant allele • q = frequency of recessive allele • p2 + 2pq + q2 = 1 • p2 = frequency of homozygous dominant genotype (AA) • 2pq = frequency of heterozygous genotype (Aa) • q2 = frequency of homozygous recessive genotype (aa)

7. Solve this story problem • In pigs, the allele for black coat is recessive to pink coats. • B = pink; b = black • Calculate q2 for the illustration shown below. • q2 = 0.25 (4/16)

8. Find q. • q = 0.5 • Find p. • p = 0.5 • Find 2pq. • 2pq = 0.5 • This means 50% of the pink pigs are heterozygous.

9. Solve this story problem • In a certain flock of sheep, 4 percent of the population has black wool and 96 percent has white wool. • If black wool is a recessive trait: • What percentage of the population is homozygous black? (q2) • What percentage of the population is heterozygous for this trait? (2pq) • What percentage of the population is homozygous white? (p2)