Sex-linked traits are characteristics that appear much more commonly in males then in females. The genes for sex-linked traits are carried on the sex chromosomes.

Within an organism's body cells, chromosomes are arranged in pairs called homologous pairs. The two chromosomes in each homologous pair are the same size and have corresponding genes for the same traits at the same locations. Each body cell has two sex chromosomes that make up one of the homologous pairs of chromosomes. In most species, there are two types of sex chromosomes, the X chromosome and the Y chromosome. Unlike other pairs of homologous chromosomes, the X chromosome is larger than the Y chromosome, and therefore the sex chromosomes do not always have corresponding genes for all of the same traits; the Y chromosome is lacking some genes that are present on the X chromosome.

In humans and many other...