#### Answer

$\frac{1}{4}$

#### Work Step by Step

P(E) = $\frac{no.\ of\ outcomes\ in\ favor}{Total\ no.\ of\ outcomes}$
A person with two sickle cell genes will have the disease, but a person with only one sickle cell gene will have a mild, nonfatal anemia called sickle cell trait.
E: Has sickle cell anemia
Favorable outcomes= {ss}
P(E) = $\frac{1}{4}$