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SAT® Subject Test in Biology

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Codominance Sickle Cell Anemia

SATBIO-E4NIYJ

Sickle cell anemia is a genetic disorder caused by a substitution mutation in the gene encoding hemoglobin, the protein on blood cells responsible for carrying oxygen. This mutation causes the hemoglobin protein to fold incorrectly, preventing the protein from carrying oxygen on the red blood cells.

Sickle cell anemia is inherited as a codominant trait, meaning that both alleles are expressed equally and that one is not dominant over the other. The allele for normal hemoglobin is represented by S, and the allele for abnomal hemoglobin is represented by s.

If two heterozygous individuals mate and produce offspring, what proportion of their offspring are expected to have fully sickled red blood cells?

A

1

B

0.75

C

0.5

D

0.25

E

0