John has sickle cell disease. Ann is normal and is not a carrier. Can their children have sickle cell disease (not sickle cell trait)? Explain your answer.

Yes, their children can have sickle cell disease. Sickle cell disease is an autosomal recessive genetic disorder, which means that a child can only have the disease if they inherit two copies of the affected gene - one from each parent. John has sickle cell disease, so he has two copies of the affected gene. Ann is normal and not a carrier, which means she has two normal copies of the gene. Therefore, all of their children will inherit one copy of the affected gene from John and one normal copy from Ann, making them carriers of sickle cell trait. If two carriers have children together, there is a 25% chance that each child will inherit two copies of the affected gene, resulting in sickle cell disease.