Question

Consider the following pedigree over four generations and mark the correct answer below about the inheritance of haemophilia.

A) Haemophilia is X-linked dominant
B) Haemophilia is autosomal dominant
C) Haemophilia is x-linked recessive
D) Haemophilia is y-linked dominant

Answer 1

Hint:Haemophilia is a largely hereditary genetic condition that impairs the capacity of the body to make blood clots, a mechanism that is important to avoid bleeding. This results in people bleeding after an injury for a longer period, quick swelling, and an increased risk of bleeding within joints or the brain.

Complete answer:
Characteristic signs differ according to severity. In general, internal or external bleeding episodes, called 'bleeds,' are symptoms. People with more severe haemophilia experience more severe and more frequent bleeding, while people with moderate haemophilia, even after surgery or severe injuries, typically experience more minor symptoms. In cases with severe haemophilia, symptoms that occur along a continuum between extreme and mild types are variable.
A condition carried by an X-linked gene is this disorder. There are two alleles for this gene. One where you do not have dominant haemophilia (H), and one where you do have recessive haemophilia (h). In women, as they have two X chromosomes, the disease is much less common. This is because if they are given one gene with haemophilia, they have a chance of having a non-hemophiliac gene from their other chromosome.

	Xh	Y
XH	XHXh	XHY
XH	XHXH	XHY

The haemophilia gene will cancel this, because they may not have the disorder. Of course, if there were two haemophilia genes given to a woman, they would have the disease. The mother (left side) in the test cross above is absolutely free of haemophilia.Father(top) is affected by haemophilia.
This is because the gene for haemophilia is not borne by the Y chromosome). In the two cases where the child may be a female, she carries the hemophilia gene, however it is counteracted by the non-hemophiliac gene, so while she would be a carrier, she would not have haemophilia.

Thus the correct answer is option (C) Haemophilia is X-linked recessive.

Note:Hemophilia is a recessive sex-linked condition. In males, these kinds of defects occur more frequently than in females.Hemophilia is more common among male children because they only inherit one X chromosome.