Question

Juan’s family has a history of sickle cell disease. His father died of sickle cell disease complications when Juan was six years old. He remembers his father being in great pain. Juan marries Gina. Gina’s maternal grandmother and paternal grandfather had sickle cell disease, but neither of her parents has the disease. Juan does not want to have children because he is convinced they will have sickle cell disease. Gina is not so sure. They have come to you for advice about having whether or not to have children. Based on your calculations of the probability of their child getting sickle cell disease, what is your advice? Show your calculations and explain your reasoning for your response. It may be helpful for you to draw pedigrees and possible Punnett squares for both Juan and Gina’s families

Answer 1

Sickle cell disease is a hereditary disease. This means that someone can get sickle cell disease if they receive the sickle genes from BOTH parents. If someone receives a sickle gene from only one parent, then this person does not have sickle cell disease, but instead has the sickle cell trait. This means that they can still pass the trait on to their offspring. Because Juan's father had sickle cell disease and Juan does not, he carries the sickle trait. Since Gina's maternal grandmother had sickle cell disease, Gina's mother had a 50 percent chance of carrying the trait. Since Gina's father doesn't have the trait, Gina thus has a 25 percent chance of carrying the trait. If Gina has a 25 percent chance of carrying the trait and Juan has a 100 percent chance, then together they have a 125/200 chance of both passing the trait on to their children. 125/200 = .625, so they would have a 62.5 percent chance of passing on this trait to their children. Although this percentage does not mean their children would definitely have sickle cell disease, I would advise Juan and Gina to weigh their options, since 62.5 is more than 50 percent.