Hardy-Weinberg Equilibrium Model

The Hardy-Weinberg model states that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors.

A population (or an allele) is not evolving if it is in Hardy-Weinberg equilibrium.

Conditions for an allele to be in Hardy-Weinberg equilibrium: These conditions are impossible in nature!

We can compare a naturally occurring population to a theoretical population in Hardy-Weinberg equilibrium to see if the natural population is evolving. A population is evolving if: Theoretical population In Hardy-Weinberg equilibrium Naturally occurring population

How to calculate phenotypic frequency in a population: 3 white 5 black 8 total mice f(white) = f(black) = 3 8 5 8

How to calculate genotypic frequency in a population: The frequency of the recessive genotype (we will call it aa) is the same as the frequency of the recessive phenotype. f(white) = f(aa) = 3 8 3 8

How to calculate genotypic frequency in a population: The frequency of the heterozygous genotype (Aa) and the homozygous dominant genotype (AA) is harder to tell. f(black) = f(Aa) = ? f(AA) = ? 5 8

The two Hardy-Weinberg formulae allow us to calculate allele frequency: p2 + 2pq + q2 = 1 p + q = 1

The Hardy-Weinberg Variables: p2 = f (AA) = f (homozygous dominant) 2pq = f (Aa) = f (heterozygote) q2 = f (aa) = f (homozygous recessive) f (Aa) Heterozygote f (AA) f (aa) Homozyous dominant Homozygous recessive p2 + 2pq + q2 = 1

p = f (AA) = f (A) q = f (aa) = f (a) p + q = 1

Using the Hardy-Weinberg equation to find f (AA), f (Aa) and f (aa): Step 1: Find q2 Step 4: Find f (aa) f (q2) = f (white) = = .36 3 8 f (aa) = f (q2) = .36 Step 2: Find q Step 5: Find f (Aa) f(q) = f (q2) = .36 = .6 f (Aa) = 2pq = 2(.4)(.6) = .48 Step 3: Find p Step 6: Find f (AA) p + q = 1 f (p) = 1 - .6 p = 1 – q f (p) = .4 f (AA) = f (p2) = .42 = .16