Question

Describe the molecular mechanism for the expression of the two alternate cellular proteins in different tissues of a heterozygote human female. Why do such alternate cellular phenotypes not appear in the female homozygote?

Answer 1

Answer- Human female have XX genotype and hence possesses two X chrmosomes per cell. One X chrmosome is derived from father (paternally inherited) and another one is derived from mother (maternally inherited).

During gene dosage compensation in humans one of the X chromosome is inactivated in females, so as to produce same amount of X chromosomal product in both sexes.

This inactivation of one X chrmosome occurs when cytodifferentiation starts in embryonic tissue of female embryo. This inactivation of either of paternally inherited or maternally inherited X chrmosome occurs randomly in embryonic cells, therefore in some cells paternally inherited X chrmosome is inactivated while in others maternally inherited X chrmosome is inactivated which leads to express of two different cellular protein in different tissues of heterzygote human females. (Here heterozygote means two X chrmosomes, one derived from each parent, produces different protein product).

But in case of homozyote human females both paternally inherited and maternally inherited X chromosomes produces same product and thus all tissues have similar protein product.