If you observe a population and find that 16% show the recessive trait, you know the frequency of the aa genotype. this means you know q2. what is the frequency of the homozygous dominant genotype in the population above?

If the population is at Hardy-Weinberg equilibrium, then the frequency of the recessive genes would be:

aa=0.16

a = √0.16 = 0.4

Then, the frequency of dominant genes would be:

0.4+q=1

q = 1-0.4 = 0.6

The frequency of homozygous dominant genotype would be:

qq = 0.6*0.6=0.36 = 36%