Explanation:
a) The allele for hemophilia is Xh and that for normal is XH.
Crossing a hemophiliac male, Xh Y, with a normal female XH XH,
- XH Xh, normal carrier female
- XH Xh, normal carrier female
- XH Y, normal male
- XH Y, normal male
b) Both parents are normal and children still having hemophilia means that the mother is a carrier.
Let's see how it'll work out if we cross a normal male with a carrier female,
XH Y × XH Xh
- XH XH, normal female
- XH Xh, carrier female
- XH Y, normal male
- Xh Y, hemophiliac male
This means that the possibility of a female being normal, a carrier or not, is 100%. The possibility of a male being normal is 50% and the possibility of him being a hemophiliac is also 50%.
Thus it's possible that all 7 sons get hemophilia as each male baby has a 50% chance of having the genotype Xh Y. And it makes sense that all the females are normal. Those females could have the genotypes XH XH, or XH Xh (carriers).
