Haemophilia

This is another sex-linked trait where the blood of the sufferer takes an abnormally long time to clot.

In the event of a cut, this results in prolonged bleeding, hence the term bleeder’s disease. 

Haemophilia is caused by a recessive gene on the X chromosome.

For instance, if a normal man is married to a carrier woman for haemophilia, there is a probability of a  that if their child is a b0y he will be a haemophiliac and if a daughter, she will be a carrier.

Let H represent the gene for normal blood clotting condition. Let h represent the gene for haemophilia.

Both genes are located on the X chromosomes e.g. X^H or X^h.

Genetic cross