recessive allele

A recessive allele is the quiet switch that only matters when both switches are off. Its effect stays hidden whenever a dominant allele is present, so the trait it specifies appears only when an individual inherits two recessive copies — one from each parent. A person with just one copy carries the allele silently and looks unaffected.

Such a silent carrier can still pass the recessive allele on, which is why a recessive trait can seem to skip generations and then reappear when two carriers have a child. About one in four of their children, on average, inherit two recessive copies and show the trait. This is exactly the 3:1 pattern Mendel observed in his pea crosses.

Recessiveness frequently reflects a loss-of-function change: when both copies are broken there is no working version to compensate, and the missing function shows up as the trait. Many inherited disorders follow this pattern, but 'recessive' is a statement about how the allele behaves in pairs, not a measure of how rare or how serious the allele is.