Sex linkage

The sex chromosomes, although mainly responsible for determining gender, carry some genes that code for a number of body functions.

These genes are described as sex-linked.

The other 22 pairs of chromosomes have the same genes in the same position on both chromosomes.

The difference in size between the X chromosome and the shorter Y chromosome means some genes appear only on the X chromosome.

The effect of sex-linked genes is more obvious in males because the X chromosome can contain genes the Y does not.

A recessive allele on the X chromosome will show in the phenotype as there is no dominant allele present to override it.

A female will have another allele on her other X chromosome which, if dominant, would mask the effect of a recessive allele.