Genetics pedigree

Given that the onset of the disease is by 40 years of age and given that all of the individuals shown are at least 45 years old except III‑2 who is only 30 years old, what is the probability that the fetus (IV­-1) will be affected?


to be honest this was a bit challenging but I managed to find an answer.

i tried both if the disease was homozygous recessive or dominant
if it was dominant I would get 50% too but when I tried if it’s homozygous recessive which made much more sense with the pedigree then the answer came up to 25 percent.
i considered individual 2 as heterozygous (not affected) because even though he might have not had the disease, if he is affected then he would have the alleles. the only difference would be that the disease won’t be showing.
i am still unsure why it wouldn’t be 50% tho because both solutions worked but I may be missing something.
let me know if it makes sense!


hey , I believe your consideration for being recessive is totally correct ,However for the first part you said that if we consider it dominant it would be %50, but based on my interpretation it is %100 healthy ,no affection .what is different?

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sorry the paper I solved this with is not with me right now but I think what I meant was not by homozygous dominant but instead heterozygous dominant which means the sick one would have to have homozygous recessive in order to be sick
but still, i may have made a mistake i will check when i can find my paper:)

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