Question

If grey fur is dominant to white fur in a rabbit population, how many possible phenotypes will there be in the offspring of a cross between two heterozygous parents

Answer 1

Allele for gray fur is A (dominant)
  Allele for white fur is a (recessive)
Genotype of heterozygous is Aa (heterozygous is gray, because its allele is dominant)
If we cross two heterozygous
Parents: Aa  x  Aa
F1: AA  Aa  Aa aa
The ratio between phenotypes is 3:1 (gray:white)
AA Aa Aa  are with gray fur
aa is with white fur