Question

Sickle cell anemia is known to run in a family. A pedigree chart for this family is shown below.

The parents are shown at the top and from left to right appear as a half-shaded circle next to a half-shaded square. The two are connected by a straight line. Below the parent pair is a vertical straight line connecting to the next row of circles and squares which are the offspring. Starting from left an unshaded square, half-shaded circle, another half-shaded circle, and a completely shaded square are shown. All of these are also connected by a horizontal straight line.

What percentage of the offspring have sickle cell anemia?

0%
25%
50%
100%

Answer 1

In the described pedigree chart showing autosomal recessive inheritance for sickle cell anemia, 25% of the offspring have sickle cell anemia, as indicated by one completely shaded square out of four offspring.

Step-by-step explanation:

Sickle cell anemia is an autosomal recessive disorder, which means that for someone to have the disease, they must inherit two copies of the sickle cell gene (one from each parent). If an individual receives only one sickle cell gene and one normal gene, they are a carrier of the trait but do not exhibit symptoms of the disease. In the pedigree chart described, half-shaded symbols represent carriers of the sickle cell trait, and fully shaded symbols indicate individuals with sickle cell anemia.

In the family described, we have four offspring: an unshaded square (a male with normal genes), a half-shaded circle (a female carrier), another half-shaded circle (another female carrier), and a completely shaded square (a male with sickle cell anemia). Therefore, 25% (one out of four) of the offspring have sickle cell anemia.