If the 1st child of V3 and V4 was affected the chance that t

If the 1st child of V-3 and V-4 was affected, the chance that their next child would be affected is:

a. 1/4 b. 1/9 c. 1/18 d. 1/36 e. 1/64 f.1/81

Solution

At the III generation, the marriage was congenial due to which 2 out 6 children were affected. Again at the IV generation, there is a congenial marriage, due which there might be a chance of an affected child at the V generation. The first child is affected and the chances of next child being affected would be 1/4.

As the fourth generation females might be a carrier for this disease, so congenial marriage increases the risk of expression of this phenotype in V generation.