X-linked recessive

X-linked recessive A mode of genetic inheritance characterized by a gene on the X chromosome being expressed only when there is no different gene present at that spot (locus) on a second X chromosome. This means that X-linked traits are expressed in males and in females who are homozygous for the gene (they have a copy of the particular gene on each of their two X chromosomes). For example, Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder. A boy with DMD has the DMD gene on his sole X chromosome. Although it is much rarer, a girl can have the DMD gene on both her X chromosomes and have DMD. See also autosomal recessive trait; X-linked dominant.