When an allele (gene mutation) is situated on a sex chromosome or allosome as opposed to a non-sex chromosome or autosome, the resulting sex-specific traits of inheritance and presentation are referred to as “sex-linked”.

Sex-linked inheritance are referred to as X-linked dominant, X-linked recessive, and Y-linked in humans. All three have unique inheritance and presentation traits based on the sexes of the child and the parent. This is how they distinguish themselves from autosomal dominance and recessiveness.

In mammals, the male is heterogametic, having one X and a Y chromosome (XY), while the female is homogametic, having two X chromosomes (XX). Sex-linked genes are those that are located on the X or Y chromosome.

A famous example of sex-linked inheritance in humans is haemophilia. The X chromosome contains a mutant gene (h) that is recessive to the normal gene and, as a result, silenced in heterozygous females. This condition causes people to lack a factor necessary for blood coagulation. Therefore, a small cut or injury can result in prolonged bleeding that results in fatality if no blood clotting factor is present. Men are more commonly affected from this condition.

Read Also:

• Sex Chromosome Abnormalities
• MCQs on Chromosomes
• Important Notes for NEET Biology – Chromosome Structure

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