What does 'aa', 'Aa' and 'AA' mean in DNA?

Question

I need to understand what these mean in order to complete my pedigree....

Answer 1

aa is homeogeneous recessice

Aa is heterogeneous

AA is homegeneous dominant

Answer 2

Could you be talking about these in reference to punnett squares? if so, A represents a dominant gene and 'a' represents the recessive gene. The combinations, aa, Aa, and AA are each organism's genotype received from the parents. So if the organism gets the genotype AA, it means that it has the dominant gene and will only pass on A or A to its offspring. Aa means it carries both genes, but A is the one that is present in the organism.  

Answer 3

In genetics, an upper-case letter designates a dominant trait, whereas a lowercase letter designates a recessive trait. In normal, Mendelian genetics, dominant traits mask the physical expression of recessive traits. aa, Aa, and AA are all genotypes, or the different types of gene combinations that are possible with only 2 alleles. Homozygous means both alleles that make up that gene are the same, whether it be aa or AA. Heterozygous means that the alleles are different, meaning Aa. Homozygous dominant means that it is the same for both alleles being dominant, or AA, and homozygous recessive means that it is both recessive alleles, or aa.

For phenotypes, or the physical expression of the gene, again, dominant masks the recessive (in Mendelian genetics - otherwise there is such thing as codominance (blood type) and incomplete dominance (roan bulls)). Both AA and Aa, because they contain a dominant allele, will show the dominant A physical trait (example: polydactyly - more than 5 fingers). Only a geneotype with aa will show the recessive trait (example: 5 fingers).