Hemophilia-In males (Man) only as the bleeder’s disease or Haemophilia occurs., In haemophilic men, the blood fails to clot, even a small injury results in continuous bleeding and can lead to death from loss of blood’. In normal man on the other hand, it takes 2 to 8 minutes for blood to clot.

Haemophilia is caused by a sex-linked recessive gene located in the

X-chrornosome. It is inherited strictly in the same manner as colourblindness i.e. its single gene in man results in disease hemophilia, whereas a woman requires two such genes for the same. The hemophilic men if they survive and reach reproductive age, produce daughters, all of them are apparently normal but genotypically they are carriers i.e. having one gene for normal condition and other for hemophilia.

showing sex-linked disease hemophilia
Hemophilia in females is very rare and it is obvious that it could not occur with same degree of severity as in man. A girl with severe bleeding would die by the time she reaches maturity. The chance of homozygous girl being born in random mating is very slight, because the frequency of hemophilic males is about one in 10,000. This means almost same frequency will be shown by the carrier females. The frequency of homozygous females exactly on the arithmetical basis will be one in 1O,OO,OO0O. This frequency is calculated when all haemophflic males survive

In birds, moths and butterflies, the female is  XY and themale is XX’ or ZZ. The gene for barred plumage is dominant over gene for non-barred plumage. This gene is placed on ‘X chromosome. Hence It shows sex linked inheritance.

When Barred female is crossed with a Non-Barred male the, F1 offspring shows all males are Barred and females are Non-Barred. This is called

criss-cross inheritance.