Recessive
An allele that is masked when a dominant allele is present
“Recessive” is a term used to describe a genetic trait that is only expressed (visible or active) when two copies (alleles) of that gene are present in an individual’s genome. In this case, the trait is said to be “homozygous recessive” because both copies of the gene are recessive.
A recessive trait can be overshadowed or masked by a dominant gene for that trait. For example, if a child inherits a dominant gene for brown eyes from one parent and a recessive gene for blue eyes from the other parent, the child’s eyes will be brown because the brown eye color is dominant and masks the recessive blue.
However, if both parents pass on the recessive gene for blue eyes, the child will have blue eyes because there are no dominant genes to mask the recessive trait.
Some examples of recessive genetic disorders include sickle cell anemia, cystic fibrosis, and Tay-Sachs disease. These diseases are only expressed in individuals who inherit two copies of the disease-causing gene (one from each parent) and not in individuals who only inherit one copy.
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