Select the incorrect statement with regard to haemophilia.

MCQ

✓
It is a dominant disease.
B
A single protein involved in the clotting of blood is affected.
C
It is a sexlinked disease.
D
It is a recessive disease.

✓

Answer

Correct option: A.

It is a dominant disease.

a
(a): Haemophilia is sexlinked disease which is also known as bleeder’s disease as the patient will continue to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of antihaemophiliac globulin or factor $VIII$ (haemophilia -$A$) and plasma thromboplastin factor $IX$ (haemophilia-$B$, Christmas disease) essential for it. As a result of continuous bleeding the patient may die of blood loss. It is geneticallydue to the presence ofa recessive sex linked gene $h$, carried by $X$-chromosome. A female becomes haemophiliac only when both of her $X$-chromosomes carry the gene $(X^hX^h)$. However, such females generally die before birth because the combination of these two recessive alleles is lethal. A female having only one allele for haemophilia $(XX^h)$ appears normal because the allele for normal blood clotting present on the other Xchromosome is dominant. Such females are known as carriers. In case of males, a single gene for the defect is able to express itself as the $Y$ chromosome is devoid of any corresponding allele $(X^hY)$.

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