Answer
A dominant allele is one that is visible even with only that allele present. A recessive allele is only visible if there are two of that allele.
Work Step by Step
The dominant allele will always be visible in the phenotype if it is present. However, if the offspring is homozygous recessive, the dominant trait will not be visible because it does not exist in the offspring. If the offspring were heterozygous, then the offspring would look identical to an offspring who was homozygous dominant because the dominant gene is always visible over the recessive.
