Which statement describes a recessive allele most accurately?

• A. It expresses only when two copies are present
• B. It masks the dominant allele when present
• C. It is always expressed whenever it occurs
• D. It is never inherited

Answer: (A)

Recessive alleles show their effect only when there are two copies present. At a gene locus, you have two alleles. If at least one allele is dominant, the dominant trait appears in the organism’s phenotype, so the recessive version isn’t visible. Only when both alleles are the recessive variant does the recessive trait manifest. Importantly, a recessive allele can still be passed to offspring—even if it isn’t displayed in the parent’s phenotype—so someone can be a carrier. This explains why the trait isn’t expressed unless two copies are present, and why recessive alleles can be inherited even when not seen.