Question

Males have hemophilia when they are hemizy-gous for a nonfunctional recessive mutant allele of the X-Iinked gene for clotting factor Vlll. Factor Vlll is normally secreted into the blood serum by cells in the bone marrow that produce it. a. Do you think that females heterozygous for the hemophilia disease allele could have hemophilia in some parts of their bodies and not others? b. If such a female "carrier" of hemophilia suffered a cut, would her blood coagulate (form clots) faster, slower, or in about the same time as that of an individual homozygous for a normal allele of the factor Vlll gene? Would the rate of clotting vary significantly among heterozygous females?

Answer 1

a. No, it is not possible.

A heterozygous female carries one copy of functional gene which is enough for the production of clotting factor. Hemophilia does not show continuous variation or polygenic inheritance and thus, its level does not depend on the number of normal alleles.

It that was the case, then all males would show hemophilia in some parts of the body as they only carry one X chromosome and thus, only one functional gene.

Thus, heterozygotes are only the carriers of the disease, they do not show any symptom of the disease.

b. In perspective of homozygosity or heterozygosity, the rate of blood clotting should be the same as both of them have functional gene. As mentioned above, it does not show continuous variation so, it will not show any increased or decreased rate of clotting in homozygotes or heterozygotes.

However, in reality, the rate of clotting depends on the concentration of clotting factor present in blood plasma. This percentage depends on the physiology of a person but not on the number of alleles present. For example, proteins or enzymes required for gene expression, et cetera.