sex linkagen.

The occurrence of the gene controlling a particular characteristic on a sex chromosome; the resulting pattern of inheritance in which a characteristic is expressed chiefly or solely in individuals of one sex.The most common form of sex linkage in humans is that involving a characteristic whose gene is carried on the X chromosome. Any distinctive or abnormal form of such a gene (e.g. causing some kinds of haemophilia and colour blindness) is expressed in males (who have only one X chromosome), but may be modified or masked in females by the presence of a second X chromosome carrying the normal form of the gene.