Answer:
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 Â Â Â Â Â Â Â RR Â Â Â Rr
r        Rr     rr
RR: healthy (25%).
Rr: Â 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 https://brainly.com/question/10605612