Question

In a family both the husband and wife are heterozygous for a condition of infantile blindness. They wish to have at least 3 children. What would be the possibility that all these children would be normal?

Answer 1

Infantile blindness is autosomal dominant disorder.
Suppose allel B' is responsible for carrying a disease.
Bb' and Bb' would be heterozygote parents. BB, Bb are all diseased.
If we cros sthem both , outcome of the offspring would be
1 BB: 2Bb : 1bb

so 3/4 = are diseased. If they plan to have thre echildren, possibility of each having a disease is 3/4
total probability = 3/4 x 3/4 x 3/4 = 0.42 = 42%