Hemophilia A is an X-linked recessive condition. It results in a lack of blood c

Question

Hemophilia A is an X-linked recessive condition. It results in a lack of blood clotting ability.

We will use XH to represent the normal allele, Xh to represent the hemophilia allele, and Y to represent the Y chromosome, which does not contain the associated gene.

If a mother is a carrier (XHXh), and a father does not have hemophilia A (XHY), what percent chance does a daughter between them have of suffering from this affliction? What percent chance does a son have?

Complete a Punnett square on your own paper to help solve this problem.

0% for daughters and 0% for sons

50% for daughters and 50% for sons

50% for daughters and 0% for sons

0% for daughters and 50% for sons

Explanation / Answer

Cross between a carrier mother (XHXh), and normal father (XHY) will have the offspring with the following genotypes.

XHXh* XHY = XHXH (normal female), XHY (normal male), XhXH (carrier female), XhY (affected male).

Thus, chances of having a daughter with the disease is 0%. The chances of having a son with the disease is 25%.

The chances of having normal son = Chances of having son* chances of having normal allele = 1/2* 1/2 = 1/4.

Chnces of having normal daughter (not carrier) = Chances of having daughter* chances of having normal allele = 1/2* 1/2 = 1/4

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