What Is a Recessive Allele

In genetics, traits are controlled by genes, and each gene has different versions called alleles. A recessive allele is a type of allele that only shows its trait when both copies of the gene are recessive. This means the trait will only appear if an individual inherits the recessive allele from both parents.

For example, imagine a gene that controls flower color. A dominant allele (represented by a capital letter, like R) might produce red flowers, while a recessive allele (represented by a lowercase letter, like r) produces white flowers. If a plant has one of each allele (Rr), the dominant allele will mask the recessive one, and the plant will have red flowers. Only when the plant has rr, two recessive alleles, will it have white flowers.

Recessive traits can be hidden for generations. This happens because someone can carry a recessive allele without showing the trait. These individuals are called carriers. For example, two parents who each carry the recessive allele for blue eyes (but have brown eyes) can have a child with blue eyes if the child inherits the recessive allele from both of them.

Recessive alleles are a key reason why genetic variation exists. They allow traits to pass silently from generation to generation and reappear under the right genetic conditions. This is also important in understanding some genetic disorders, which can only appear when both alleles are recessive.

Fun Fact: Blue eyes are caused by a recessive allele—and scientists believe all people with blue eyes share a single common ancestor who first had that mutation!