Characters determined by a gene located on only the X-chromosome are said to be sex-linked. Such traits show a different pattern of inheritance in males and females. For example, a recessive allele on the X-chromosome
• would be masked in a female if the corresponding allele on the other X-chromosome is dominant;
• would always be expressed in a male because the Y-chromosome does not have a corresponding(active) allele.
Thus, the female may posses a homozygous or heterozygous allelic pair for a sex-linked character, but a male will only have one allele for it.
