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Recently a baby girl has been reported to suffer from heamophilia. How is it possible? Explain with the help of a cross.

Haemophilia is a recessive, sex linked disease. If the baby girl is suffering from haemophilia that means mother is a carrier of haemophilia and father must be suffering from a disease. This can be explained with the help of a cross-
XHY (Father) X  XHX (Mother)
XHXH  XHX   XHY  XY (Gametes)
 (​A)        (B)     (C)    (D)

A is a female child and is haemophilic.
B is a female and is a carrier of a disease.
C is a male child and is suffering from a disease.
D is a male child and is normal.

 

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for a girl to be hemophilic the girl's mother must be a carrier and the fater must be haemophilic ..........................

parent --------- H^A H^T(mother) H^T H^T(father)

progeny-------------------- H^A H^T , H^A H^T , H^TH^T , H^T H^T

so u see that probability of progeny being haemophilic increases by 50%

but if it had been a mother carrier and a father normal or carrier it would have been just 25 %

the female suffres from haemophilia when the haemophilic X chromosome from father combine to the haemophilic X chromosome of mother

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