In regions where malaria is prevalent, the S allele is beneficial because:a. it prevents mosquitoes from releasing Plasmodium, the mosquito that causes malaria, into the blood. b. it improves the ability of the hemoglobin to carry oxygen. c. it causes red blood cells to distort, which makes them less hospitable to Plasmodium, the parasite that causes malaria. d. it improves the ability of the immune system to fight Plasmodium, the parasite that causes malaria.

c. it causes red blood cells to distort which makes them less hospitable to Plasmodium, the parasite that causes malaria

Explanation:

The normal haemoglobin is a tetramer of four globin chains (2 alpha and 2 beta chains).

When a gene mutation occurs, i. e the substitution of a single nucleotide which leads to the formation of valine instead of glutamate, the hemoglobin would become sickle shaped. This gives rise to the Hb S allelle.

Therefore in malaria-endemic regions, the S allelle is beneficial because the distorted or sickle-shaped red blood cells would be less hospitable to Plasmodium and this would confer protection on the host.