Final answer:
The frequency of genotype aa is 0.4; allele A frequency is 0.6; allele a frequency is 0.4. The most advantageous genotype cannot be determined without context, and the phenotype of Aa depends on the type of dominance but often resembles AA if A is completely dominant.
Step-by-step explanation:
The frequency of genotype aa is 4 out of 10, or 0.4. The allele A frequency is 1 - q (if q is the frequency of allele a), and can be calculated by counting the total instances of allele A which is 12 in 20 total alleles, so the frequency of allele A is 0.6. The allele a frequency can be calculated similarly; it appears 8 times in 20 alleles giving us a frequency of 0.4.
Without additional information, we cannot definitively tell which genotype is most advantageous; natural selection would determine that based on environmental contexts and other factors. In terms of phenotype resemblance, unless we know the trait's dominance, Aa can resemble either AA or aa. Usually, if A is the dominant allele, Aa would phenotypically resemble AA, if 'A' is incomplete dominant or codominant, then Aa may have an intermediate or a combination of traits.