Which of the Following Calculations Require the Use of the Addition

Multiple Choice

Which of the following calculations require the use of the addition rule of probability?

A) Calculate the probability of black offspring from the cross AaBb × AaBb, where B is the symbol for black.
B) Calculate the probability of children with both cystic fibrosis and polydactyly when parents are each heterozygous for both genes.
C) Calculate the probability of each of four children having cystic fibrosis if the parents are both heterozygous.
D) Calculate the probability of a child having either sickle-cell anemia or cystic fibrosis if parents are each heterozygous for both.