X-linked recessive

Definition

X-linked recessive is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males who are necessarily hemizygous for the gene mutation (i.e., they have only one X chromosome) and in females who are homozygous for the gene mutation (i.e., they have two copies of the gene mutation, one on each X chromosome). Females with one mutated gene on an X chromosome are typically carriers and usually do not show symptoms due to having another normal copy of the gene on their other X chromosome.

Related terms

Hemizygous:

Having only one allele of a gene or DNA sequence in an otherwise diploid cell; often applies to genes on the sex chromosomes in males.

Carrier: An individual who has one copy of a recessive allele that causes disease in the homozygous state but does not exhibit disease symptoms; carriers can pass the allele to their offspring.

Phenotype:

The set of observable characteristics or traits of an organism that result from the interaction of its genotype with the environment