Genetic Counseling: Disease Probability in Marriage - Carrier & Homozygous Recessive

If a man is carrying an allele for a disease and marries a woman who is homozygous recessive for the same disease, the probability of their offspring having the disease is 50%.

This is because the man will contribute one copy of the disease allele to each offspring, and the woman will contribute one copy of the recessive allele. When these alleles are combined, they will produce offspring who are either heterozygous carriers of the disease (50%) or homozygous recessive for the disease (50%).

The heterozygous carriers will not have the disease themselves, but they will be able to pass on the disease allele to their own children. The homozygous recessive offspring will have the disease.