Sickle cell disease is a recessive trait which causes a deformation in red blood cells due to a mutation in the gene that codes for hemoglobin. Consider a father and a mother BOTH with the genotype Hh, where H is the normal hemoglobin gene, and h is the gene that codes for the defective hemoglobin. What percent of their children will have the genotype hh, which means they will have the full-blown disease?