In couples where each person is heterozygous for the sickle-cell gene, there is a probability of 0.25 that any child of the couple will have the disease. A husband and wife, who are both heterozygous for sickle-cell, are planning to have a family of four children.
What is the probability that their first child will not have sickle-cell anemia?
What is the probability that none of their four children will have sickle-cell anemia?
What is the probability that at least one of their children will have sickle-cell anemia?