Using a punnet square (courtesy of grigore mendel), you will find that crossing Aa Aa creates theoretical offspring that are 25% AA, 50% Aa, and 25% aa.
I think it is 25%. When you draw a genetic diagram for Aa and Aa the results are AA - homozygous dominant, Aa - heterozygous dominant, Aa - heterozygous dominant and aa - homozygous recessive. So that is 1 out of 4, therefore 25%.
