The answer is 3:1.
A - the dominant allele
a - the recessive allele
The parental generation (P) is AA and aa:
P AA x aa
F1 Aa Aa Aa Aa
F1 is the first generation of offspring. After their cross, we get the second generation of offspring:
F1 Aa x Aa
F2 AA Aa Aa aa
So we have 3 dominant phenotypes (AA, Aa, and Aa) and 1 recessive phenotype (aa). The ratio is 3:1
