Which type of mutation causes sickle cell anemia?
a. silent
b. missense
c. insertion
d. frameshift

Ans. (b). missense.

Sickle cell anemia is an inherited blood disorder, due to defect in oxygen-transporting protein, hemoglobin. It is caused by a mutation in a gene that codes for hemoglobin that substitutes GAG codon (that codes for glutamic acid) with codon GUG (that codes for valine).

It is known as a missense mutation, which leads to formation of a non-functional or defected protein (hemoglobin). The defected hemoglobin gets polymerized and forms fibers that give sickle-shape to the red blood cells.

Thus, the correct answer is option (b).