Which statement describes a recessive allele?

• A. It is always expressed
• B. It is always masked by dominant
• C. It is never found in heterozygotes
• D. It shows its trait only when the dominant allele is not present

Answer: (D)

Recessive alleles are expressed only when an organism has two copies of that allele and there is no dominant allele to mask it. This means the trait appears only when the dominant allele is not present, i.e., in a homozygous recessive genotype. The idea is that a dominant allele overrides the recessive one in heterozygotes, so the recessive trait isn’t shown there. That’s why this statement is the best: it captures that the recessive trait shows up only when there isn’t a dominant allele to mask it. The other options are less accurate because a recessive trait isn’t always expressed, a dominant allele can mask it in heterozygotes, and a recessive allele can be carried in heterozygotes without expressing the trait.