How to calculate allele frequency in the F2 generation

Significance of the Hardy-Weinberg Equation

By the outset of the 20th century, geneticists were able to use Punnett squares to predict the probability of offspring genotypes for particular traits based on the known genotypes of their two parents when the traits followed simple Mendelian rules of dominance and recessiveness. The Hardy-Weinberg equation essentially allowed geneticists to do the same thing for entire populations.

It is important not to lose sight of the fact that gene pool frequencies are inherently stable. That is to say, they do not change by themselves. Despite the fact that evolution is a common occurrence in natural populations, allele frequencies will remain unaltered indefinitely unless evolutionary mechanisms such as mutation and natural selection cause them to change. Before Hardy and Weinberg, it was thought that dominant alleles must, over time, inevitably swamp recessive alleles out of existence. This incorrect theory was called "genophagy" (literally "gene eating"). According to this wrong idea, dominant alleles always increase in frequency from generation to generation. Hardy and Weinberg were able to demonstrate with their equation that dominant alleles can just as easily decrease in frequency.