Godfrey Hardy ( ) Wilhelm Weinberg ( ) Hardy-Weinberg Principle p + q = 1 Allele frequencies, assuming 2 alleles, one dominant over the other p= frequency of dominant allele q= frequency of recessive allele p² + 2pq + q² = 1 Genotype frequencies P 2 = frequency of homozygous dominants 2pq = frequency of heterozygotes q 2 = frequency of homozygous recessives

These equations allow us to calculate allele frequencies in a population. Of course allele frequencies in a population can change due to any of the following factors: Gene flow Mutation Natural selection Genetic Drift Thus, the Hardy-Weinberg equations are only valid for a population that is not undergoing any of these changes i.e. not evolving. They do inform us if a population is in equilibrium and we can use them to tell if a population has evolved.

For a population to be in equilibrium (not evolving), the following factors have to be present: No mutation No natural selection No gene flow into or out of then population Large population to avoid genetic drift problems All mating is totally random and is always successsful Simulation of Hardy-Weinberg Equilibrium conditions: e4e_15-6-OSU.swf If all of these conditions are met, a population is said to be in genetic equilibrium and is not evolving. If we can detect a change in allele frequency, however, we can conclude that a population has evolved.

Hardy –Weinberg can also be used to demonstrate why it is that recessive alleles do not disappear in populations in genetic equilibrium: main_body.asp?s=23000&n=00020&i= &v=chapter&o=|00010|00020|00030| 00060|&ns=0&t=&uid=0&rau=0

Sample H-W question q1d.html