Sickle cell anemia is produced by a genetic defect in the amino acid sequence of hemoglobin. Persons who are homozygous for this allele have abnormal red blood cells, which characterize the disease. The blood cells of heterozygous persons appear normal and they are considered carriers. A test reveals that a man is heterozygous for the sickle cell allele but his wife is homozygous normal.
What is the probability of their children will be carriers of the disease allele?