What is the probabilty that Amit will have
1-a child who carries the recessive allele for Niemann -pick disease type A ?
2- a child who neither has nor carries the recessive allele for Niemann-pick disease type A.
3- a child with Niemann-pick disease type A
Amit is a healthy man in his forties. his family shows no sign of Niemann-pick disease type A ;thus he is not a carrier.
First, we have to note that Niemann-Pick Disease is recessive - this means that for a person to get the disease, he must have both copies or alleles of the gene.
We are given that Amit (and his family) has no sign of the disease, and is thus not a carrier. His genotype is NN (where N is the dominant non-Niemann-Pick disease allele, while n is the recessive allele for the disease).
Let us consider three cases: Case 1 - Amit's wife is a non-carrier (NN), Case 2 - Amit's wife is a carrier (Nn), Case 3 - Amit's wife has the disease (nn).
Case 1: NN x NN - There is 0 possibility that the offspring will have the disease. There is also 0 possibility that the offspring will be a carrier. In short, the offspring is sure to be homozygous dominant.
Case 2: NN x Nn - The possible offpsrings are NN, NN, Nn, Nn. Hence, there is still 0 possibility that the offspring will have the disease (since it is recessive). There's a 50% (1/2) chance that the offspring will be a carrier; and a 50% that the offspring will be homozygous dominant.
Case 3: NN x nn - The offspring wil all be carriers (Nn) - 100%. None of them will have the disease.