Human Heredity 11th Edition by Michael Cummings

Exercise 7

Sickle cell anemia (SCA) is a human genetic disorder caused by a recessive allele. A couple plan to marry and want to know the probability that they will have an affected child. With your knowledge of Mendelian inheritance, what can you tell them if (1) each has one affected parent and a parent with no family history of SCA or (2) the man is affected by the disorder but the woman has no family history of SCA?