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. They have come to their doctor Melesija for advice about whether or not to have children. Based on calculations of the probability of their child getting sickle cell disease, what advice would be given?

Answer 1

Juan father has the sickle cell trait. Gina's maternal grandmother shows the trait and Gina's mother would have inherited it, since she is heterozygous. Gina's paternal grand father shows the trait and Gina's father inherited it as he is also heterozygous.

The chances of Gina to inherit the trait is 25%

(1/2 from both parents)

1/2 + 1/2 = 1/4 equivalent to 25%

Since Gina do not show the trait. A 50% probability for Gina to have it cannot be ruled out since she's not homozygous and there is a 25% probability of being free from the trait.

Take, both Gina and juan to be carriers

HbA HbS x HbAHbS

(Shown in image 1)

We could see a 25% of probability of the trait, 50% chances and 25% of lacking the trait.

Assume Gina is free from the trait and Juan is a the carrier,

HbA HbS x HbAHbA

(Shown in image 2)

The resulting offspring would be at a 50% normal and 50% carriers and none are affected.

My advise for Juan and Gina is to be tested to affirm the likelihood of the trait being present or not as this will allow them plan for giving birth offspring rightly.