[lynk]

The correct answer is 50%
because the parents of our patients had a stillborn with hydrops fetalis it means that they must both have the alpha genes in cis-configuration --,--/a,a.
So our patient must have got --,--/a,a as he has no Heinz bodies (so he's alpha thalassemia minor which means he got one normal allele from one parent and another cis-deleted allele from another parent)
So our patient has a 50% chance of giving the abnormal alleles and 50% chance of giving the normal alleles.

can someone show me the math here pls? I dont get the 50% unless it was an AD disorder, but as thalassemia is AR I come up with the same 25%