How is an allele frequency different than a genotype?

The frequency of an allele is the total number of alleles of that type in a population where as genotype is the alleles present in all individuals in a population. The Hardy-Weinburg principle and its associated equations allow simple calculations of gene frequency. The basic equation is p+q=1: where p and q represent the dominant and recessive alleles. It is also simple to substitute the letters associated with the alleles you are dealing with for p and q.

For example: If dealing green versus yellow where green is dominant and yellow is recessive green would be G and yellow would be g. Therefore G+g=1.

In this example 40% of the population is yellow or 0.4. This means that g2 = 0.4 and this makes

g = 0.63 (rounded off). Therefore 63 percent of the alleles for this trait are for yellow and 37 percent of the alleles in the population are for green. Since G+g=1 we know that 1.0-0.63=0.37 which is G.

So 40 percent of the population is gg, it's genotype, but the frequency of the g allele is 63 percent'

Likewise 60 percent of the population is GG or Gg but the frequency of G is 37 percent.

There is a secondary equation that allows the calculation of percentages of GG and Gg as well with GG at 13.7% of the population and Gg at approximately 46.6% of the population. gg would be at 39.7%