3. Sickle cell anemia is caused by a genetic defect in coding for the amino acid sequence of hemoglobin, causing abnormal red blood cells. The blood of heterozygous persons appear normal, but when it is held under low oxygen concentration, the red blood cells become sickle shaped. A young man has a sister who died of sickle cell, and he is concerned about the possibility of the condition appearing in his children. When his blood is placed under low oxygen concentration the cells become sickled, but those of his wife do not. What is the probability of their children having the disease? How many of their children are likely to be carriers?