Answer:
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.
