Gene Pool: All the genes of all the members in a population. Allele Frequency: Percent of each allele in the population. Genetic Equilibrium: Allele frequencies remain the same from one generation to the next.

The Hardy-Weinberg Theorem States the allele frequencies remain constant (Hardy- Weinberg Equilibrium) unless acted upon by outside agents. It best describes a nonevolving population. Very useful to establish baselines in populations. Godfrey Hardy ( ) Wilhelm Weinberg (1862 – 1937)

Hardy Weinberg Theorem Populations remain stable under the following five assumptions. 1. Populations must be large Genetic Drift: allele frequencies change as a result of random events or chance

2. No Migration

3. Random Mating

4. No Mutations

5. No Natural Selection If one or more of these conditions are not met, EVOLUTION occurs.

Tasters or Non-tasters?? A = tastersa = non-tasters p+ q = 1 PhenotypesAllele Frequency Tasters (p 2 + 2pq ) Nontasters (q 2 ) pq #%#% Class Population N. American Population.55.45

Hardy Weinberg Equation To estimate the frequency of alleles in a population, we can use the Hardy-Weinberg equation. According to this equation: p = the frequency of the dominant allele (represented here by A) q = the frequency of the recessive allele (represented here by a) For a population in genetic equilibrium: p + q = 1.0 (The sum of the frequencies of both alleles is 100%.) (p + q) 2 = 1 so p 2 + 2pq + q 2 = 1 The three terms of this binomial expansion indicate the frequencies of the three genotypes: p 2 = frequency of AA (homozygous dominant) 2pq = frequency of Aa (heterozygous) q 2 = frequency of aa (homozygous recessive )

Example Screech owls are found in two different color patterns, red and gray. Scientists have raised and bred these owls in captivity. The scientists mated red to red, red to gray and gray to gray. The red to gray mating usually gave equal numbers of red and gray offspring but sometimes gave only red offspring. A population survey done in Pennsylvania showed the population to be composed of 51% red and 49% gray owls a. Which gene is dominant? b. Calculate the frequency of each allele. c. Calculate the frequency of each genotype. d. Suppose the frequency of each gene (allele) for red feathers is.42 ten years later in the same population. What could have caused the change in the gene frequency?