Question

What is sex linkage? Explain color blindness and haemophilia?

Answer 1

Sex linkage or sex-linked inheritance is the phenomenon of phenotypic expression of an allele which is linked to a sex chromosome. The expression of an allele is dependent on the sex of an individual.

Color Blindness: It is a sex-inked disorder where the person cannot distinguish between red and green colour. It is caused by a recessive gene located on X chromosome. It is mostly expressed in males, rarely seen in females. The genotype of an individual who is colorblind and the carrier will be:
Carrier female: X${}^c$X

Colour blind male: X${}^c$Y

Colorblind female: X${}^c$X${}^c$.

Haemophilia: It is a hereditary disorder in which blood does not clot. It is X-linked recessive disorder. It is also called as bleeder's disease. The gene for haemophilia is located on a non-homologous region of the X chromosome but their alleles are absent in Y chromosome. The genotype of an individual who is colorblind and the carrier will be:

Haemophiliac female: X${}^h$X${}^h$
Haemophiliac male: X${}^h$Y

Carrier female: X${}^h$X.