For a normal husband and wife the first child was diagnosed to have cystic fibrosis. What is the percentage of chances for the second child be affected -

Ans. is 'c' i.e., 0 o Cystic fibrosis is an autosomal recessive disorder. o If husband and wife are clinically normal and the child has developed the disease that means both husband & wife are carrier. o 25% will be affected and 75% will be phenotypically normal. o If one child is already affected, the chance for the disease in the second offspring is zero.