Question

${{X}^{h}}$ is the chromosome with gene for haemophilia and X is the chromosome with normal gene. Which of the following individuals will act as a carrier for haemophilia?
A. ${{X}^{h}}Y$
B. $XY$
C. $X{{X}^{h}}$
D. None of the above

Answer 1

Haemophilia is a disease in which the person’s clotting mechanism is slow and ineffective. In addition, only female carriers are responsible for the disease to be inherited by their children.

Complete answer:
An inherited genetic disorder that impairs the body's ability to make blood clots is called haemophilia. Individuals suffering from haemophilia result in bleeding for a long period of time. Females consist of two X chromosomes and males consist of one X chromosome and one Y chromosome. Haemophilia is an X-linked recessive disorder as the mutations occur in the X chromosome. As a female has two X chromosomes even if the female is carrying the defective chromosome they will not be affected as the other X chromosome which is equivalent to the dominant allele will produce the necessary clotting factors to make blood clots. So, only females can act as carriers with one defective gene in the chromosome X that is ${{X}^{h}}$. So, the carrier females have $X{{X}^{h}}$ chromosomes. The males cannot act as carriers as they have only one X chromosome. If they inherit the defective chromosome from their mother, they will be the sufferer carrying ${{X}^{h}}Y$ chromosome. A carrier mother has fifty percent chances of transferring the faulty X chromosome to her daughter whereas, a father affected with haemophilia will surely infect his daughter bypassing the faulty chromosome.

So, the option C: $X{{X}^{h}}$ is the correct answer as the carrier is a female with the faulty X chromosome.

Note: Though haemophilia is an inherited genetic disorder it can also be caused due to mutations in the gene of a healthy person. For families with haemophilia are recommended to have prenatal testing such as amniocentesis.