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  4. If father shows normal genotype and mother shows a carrier trait for haemophilia:

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Q. If father shows normal genotype and mother shows a carrier trait for haemophilia:

KCETKCET 2012Principles of Inheritance and Variation

Solution:

Haemophilia is a sex-linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progenies, hence shows criss - cross inheritance pattern. It is genetically due to recessive sex - linked gene h carried by X chromosome. A female becomes haemophiliac only when both its X chromosomes carry the gene$ (X^h X^h)$ whereas in case of males, a single gene for the defect is able to express itself $(X^h Y)$. If father is normal (X Y) and mother is carrier $(X^h X)$ then the probabilities for active disease in offsprings are illustrated in the cross given below:
Hence, a male offspring has 50% chance of active disease,
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