recessive trait

A recessive trait is one that only appears when both copies of its allele are present. It is the quieter voice in the pair: its message gets through only when there is no dominant allele talking over it, so it can stay hidden for generations and then suddenly reappear.

Because most cells carry two alleles per gene, a recessive trait shows up only in individuals who inherited the recessive allele from both parents. A person with one recessive and one dominant allele does not show the trait but can still pass the recessive allele on; such a person is called a carrier.

This hiding explains a familiar pattern: two parents who each silently carry a recessive allele can have a child who shows the trait even though neither parent does. Many recessive conditions, such as cystic fibrosis, follow exactly this route through families that had no obvious history of them.

Recessive does not mean rare, weak, or harmful. Plenty of perfectly ordinary traits are recessive, and a recessive allele can be very common in a population. The label simply describes that the trait is masked whenever a dominant partner allele is present in the same individual.