If there is a history of haemophilia in the family, the chances of male members becoming haemophilic are more than that of the female.

(a) Why is it so?

(b) Write the symptoms of the disease.

(a) Haemophilia is a genetic disorder i.e., X-linked recessive disorder and is caused by a recessive gene located on X-chromosome.

Females have two X chromosomes, so for a female to get Haemophilia, both the X chromosomes should be have mutant gene. This is not always possible.

While males have just one X chromosome and they are affected by Haemophilia when only one X chromosome have mutant gene. So they have higher chances of getting affected in comparison to females.

This is because atleast one of the two X chromosomes can have normal gene gene for each type of cone. And as the male has just one X chromosome, so missing gene can lead to Haemophilia.

X chromosome comes from mother and never from father, so heterozygous female (carrier) for haemophilia may transmit the disease to sons.

As we know the defective gene is on X chromosome, if mother is affected with Haemophilia, she passes Xh to the son he suffers. If she passes Xh to the daughter, the daughter has the other X chromosome from father to make it heterozygous so the daughters escape Haemophilia.

Hence, if there is a history of haemophilia in the family, the chances of male members becoming haemophilic are more than that of the female.

(b) The symptoms of haemophilia are:

- The blood does not clot in a haemophilic patient after an injury as the patient lacks blood clotting factor.

- Non stop bleeding after an injury

The haemophilic patient the single protein which is part of cascade of proteins required for clotting of blood is affected.