Question

Write a note on bleeder’s disease and its inheritance with a suitable chart.

Answer 1

Haemophilia (Bleeder’s disease):

1. Haemophilia is an X-linked recessive disorder in which blood fails to clot or coagulates very slowly.
2. The genes for normal clotting are dominant over the recessive genes for haemophilia.
3. The person having a recessive gene for haemophilia is deficient in clotting factors (VIII or IX) in blood.
4. Even minor injuries cause continuous bleeding, hence haemophilia is also called bleeder’s disease.
5. The recessive gene for haemophilia is located in a non-homologous region of the X chromosome.
6. As there is no corresponding allele on the Y chromosome to suppress its expression, so men suffer from this disease.
7. Women suffer only when both X chromosomes have recessive genes (alleles).

1. If a haemophilic male (X^h Y) marries a female with the normal clotting of blood (X^HX^H), then all the offspring will show normal clotting of blood. The sons will have normal clotting of blood, but daughters will be carriers for the disease. The carriers have normal clotting of blood.
   
2. When a carrier woman (X^HX^h ) marries a normal man (X^HY), then all the daughters will have normal clotting of blood but half of them will be carriers for the disease. Half the sons will be haemophilic while the remaining will have normal clotting of blood.