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 the next row of circles and squares which are the offspring. Starting from the left an unshaded square, half-shaded circle, another half-shaded circle and a completely shaded square are shown. All these are also connected by a horizontal straight line.

What percentage of the offspring have sickle cell anemia?

Group of answer choices

100%

0%

50%

25%

Answer 1

25%.

Explanation: Both parents are carriers (heterozygous). A carrier × carrier cross (Aa × Aa) yields offspring genotypes in a 1:2:1 ratio (AA : Aa : aa), so 25% (1/4) are affected (aa). In the pedigree 1 of the 4 children is fully shaded (affected).