In genetics and genomics, a carrier is generally used to describe an individual who has a genomic variant associated with a genetic condition, but does not have the condition themselves.
Use in clinical context
Carriers for a recessive condition only have one copy of the variant associated with the condition and therefore do not have the condition themselves. The chance of them passing this variant to each child at conception is 1 in 2 (50%). If only one parent is a carrier, each child has a 1-in-2 (50%) chance of being a carrier themselves, but can never be affected with the condition. If both parents are carriers for the same condition, then each child has a 1-in-4 (25%) chance of inheriting two copies of the variant and therefore being affected by the genetic condition.
Carriers of a balanced chromosomal translocation may have children who have no translocation present, the same balanced translocation, or an unbalanced translocation where genetic material is lost or gained. Unbalanced translocations always result in chromosomal conditions.
Females can be carriers of X-linked conditions. Female children who inherit the variant will also be carriers, while male children will develop the associated condition. Carriers of X-linked conditions usually do not have any signs of that condition, though there are some circumstances where carriers may have milder symptoms or subtle features of the condition.
Chromosomal condition | Chromosome | Genetic/genomic variation | Translocation