Question

If an individual with a dominant phenotype is crossed with an individual with a recessive phenotype, 4 of their 9 offspring show the recessive phenotype. What is the genotype of the first parent?

Options

• AA

• Aa

• aa

• Answer cannot be determined from this information

Answer 1

Aa

Explanation:

Since the recessive phenotype appears in some offspring, the dominant phenotype parent must carry one recessive allele. A homozygous dominant parent (AA) would produce only dominant phenotype offspring when crossed with a recessive (aa) individual. The observed fraction of recessive offspring indicates a heterozygous (Aa) first parent.