Which among the following statement is incorrect about haemophilia ?

This is a sex linked dominant disease .

The correct answer is Option (1) - This is a sex-linked dominant disease."

Hemophilia is not a sex-linked dominant disease; it is a sex-linked recessive disorder. Hemophilia is caused by a mutation in genes located on the X chromosome, and it primarily affects males. The gene for hemophilia is recessive and located on the X chromosome. Because males have only one X chromosome, if they inherit the affected X chromosome from their mother, they will display the hemophilia trait. Females need to inherit two affected X chromosomes (one from each parent) to express the disorder since they have two X chromosomes. Carrier females (heterozygous) are usually asymptomatic but can pass on the affected gene to their offspring.

This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia may transmit the disease to sons. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life).