Chapter 11.4, Problem 50E

Exercises 49-54 deal with sickle cell anemia, an inherited disease in which red blood cells become distorted and deprived of oxygen. Approximately 1 in every 500 African-American infants is born with the disease; only I in 160,000 white infants has the disease. A person with two sickle cell genes will have the disease, but a person with only one sickle cell gene will have a mild, nonfatal anemia called sickle cell trait. (Approximately 8%-10% of the African-American population has this trait.)

		Second Parent
				S	s
First	S	SS	Ss
Parent	s	sS	ss

If we use s to represent a sickle cell gene and S a healthy gene, the above table shows the four possibilities for the children of two Ss parents. Each parent has only one sickle cell gene, so each has the relatively mild sickle cell trait. Find the probability that these parents give birth to a child who

has sickle cell trait.