Maintaining Genetic Variation (Population Equilibrium )

Populations have TWO competing factors:

Remaining stable (not evolving)

vs

Changing (evolving)

Hardy Weinberg Equilibrium

“ In the absence of outside forces, the frequency of each allele in a population will NOT change as generations pass. ”

Hardy-Weinberg PrinciplesThe following factors will help to keep

population gene pools stable, that is, these

factors will prevent evolution from occurring:

1.No Selection (natural, artificial or sexual)

2.No Mutation (or any other gene changes)

3.No Gene Flow (no migration)

4.Random mating (no mate selection)

5.Large population size (keeps new genes low in number)

Recall that….The driving forces or mechanisms of

evolution are exactly the opposite, that is,

the following factors will cause evolution

(changes in gene frequencies) to occur:

1.Selection (natural, artificial or sexual)

2.Mutation (or any other gene changes)

3.Gene Flow (migration)

4.Non-Random mating (mate selection)

5.Small population size (new genes will have a greater chance to be passed on)

Hardy Weinberg Equation• A mathematical equation that helps

evolutionary biologists figure out if a population gene pool has remained stable or if it has evolved.

p2 + 2 pq + q2 = 1

• Where p = the frequency of the dominant allele• Where q = the frequency of the recessive allele• Where pq = the frequency of heterozygotes

Using the Hardy-Weinberg Equation

If the frequency of allele “a” is 7%, Find the frequency of:

allele “A”, as well as genotypes AA, Aa, and aa.

A: 100% - 7% = 93% (1.0 – 0.07 = 0.93)

AA, Aa and aa:A (0.93) a (0.07)

A (0.93)

AA

0.8649

Aa

0.0651

a (0.07)

Aa

0.0651

aa

0.0049

Teddy Graham Lab

Watch the frequency of Happy vs. Sad Bears change before your eyes!!