: Sex linkage is the phenotypic expression of an allele that is related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of expressing the trait. Since, in humans, there are many more genes on the X than there are on the Y, there are many more X-linked traits than there are Y-linked traits.
In mammals, the female is the homogametic sex, having two X chromosomes (XX), while the male is heterogametic, having one X and one Y chromosome (XY). Genes that are present on the X or Y chromosome are called sex linked genes.
Autosomal: Pertaining to a chromosome that is not a sex chromosome; relating to any one of the chromosomes save the sex chromosomes.
People normally have 22 pairs of autosomes (44 autosomes) in each cell together with two sex chromosomes (X and Y in the male and XX in the female).
