genetics doubt - senorita18

[ArchivalUser]

Can anybody explain the phenotypic calculation??? That was my initial ques

[ArchivalUser]

@djdlbhp provided the answer. Probability of phenotypically normal would be 40%.

Here is the explanation. In the above scenario, if the question asks what is probability that a child will be phenotypically abnormal (and the disease is autosomal dominant), then you take 0.75 (3 out of 4 possibilities in the punnet square give you an abnormal genotype) and multiply by 0.80 penetrance) and you get 0.60 (60% probability of a disease phenotype).

If the question asks you about the probability of the normal phenotype, then you simply subtract 60% from 100% and you get 40% (1 - 0.60).