noun, plural: sex linkages
The manifestation of certain traits as an outcome of the expression of particular genes in the sex chromosome is referred to as sex linkage. There are certain characteristics or traits that are apparently expressed more frequently in one sex than the other. For example, hypertrichosis of ears is observed in males due to patrilineal inheritance. This only shows that the genes in the sex chromosomes have control in the expression of certain characteristics of an individual. The sex chromosomes include genes that are not only for sex determination. And because of this, there are male or female traits that seem to be coupled with other traits.
In humans, there are two forms of sex linkage: (1) X linkage and (2) Y linkage. The difference lies on the type of sex chromosome involved. In particular, X linkage is a sex linkage involving the X chromosome whereas Y linkage is a sex linkage involving the Y chromosome. Since the X chromosome bears more genes than the Y chromosome there are more traits that are X-linked than Y-linked.