14. Pat and Tracy each have a sibling who has the recessive trait of sickle cell disorder. Neither Pat. Tracy or
any of their parents have the disorder, yet none have been tested to reveal the trait. Based on this
"incomplete" information, calculate the probability that if Pat and Tracy have a child, the child will have sickle
cell disorder.

Since sickle cell disease is a disorder with an autosomal dominant inheritance pattern, and in light of the lack of data, it could be said that the only way for Pat and Tracy to have a child with sickle cell disease is for both of them to be healthy carriers of the gene, with a 25% probability.

Explanation:

Considering that both Pat and Tracy each have a sibling with a sickle cell trait and that both they and their parents are healthy, it must be assumed that some of their parents are healthy carriers:

Alelles       R         r

R              RR       Rr

r               Rr        rr

RR: healthy (25%).

Rr:  healthy carrier (50%).

rr: sickle cell disease (25%).

If Pat and Tracy are healthy carriers of the gene that determines sickle cell disease, the chance of having a child with the disease is 25%.

Learn more:

Autosomal recesive inheritance link