a woman whose father had hemophilia and whose mother was normal married a man whose father did not have hemophilia but whose mother did . if the couple's first child was a son what are the chances that he would show the trait of hemophilia?

Answer 1

recall: human chromosome is represented as XX for females and XY for males. for hemophilic people, h is assigned next to the X chromosome (note, hemophilia is carried or present only on the X chromosome).

Ok..the father of the woman (the mother of the boy) has hemophilia so has genotype; XhY

mother of the woman has no hemophilia so she is XX.

the grandparent from the father is not hemophilic and so XY, whereas the grandmother is hemophilic and so XhXh.

Ok, now use cross each grandparents and see if the couples are infected;

The mother's;

father x mother = XhY x XX = XhX, XhX, Xy and Xy. So the mother of the boy is infected because 100% of the females are infected (XhX) and so she has XhX genotype.

The father's;

father x mother = XY x XhXh = XhXh, XX, XhY, XhY. So yeb, the father is also infected with a genotype XhY.

Finally, we cross the couples together

father is XhY and mother is XhX;

XhY x XhX = XhXh, XhX (carrier), XhY and XY. So, the chances are;

2/4 infected female i.e. 50%
1/4 infected male i.e. 25%
1/4 no infected male i.e. 25%

so a son would have 25% chance of getting the trait.

...see if that helps you..