In some human populations,the proportion of individuals who are heterozygous for the sickle cell allele is much higher than would be expected by chance alone.Why?
A)Individuals with two normal alleles have an advantage over heterozygous individuals.
B)Individuals with two harmful alleles have an advantage over heterozygous individuals.
C)Individuals with two harmful alleles have an advantage over individuals with two normal alleles.
D)Heterozygous individuals have an advantage over individuals with two normal alleles.

Question

Quizplus · Accepted Answer

In areas where malaria is prevalent, heterozygous individuals for the sickle cell allele have an advantage over individuals with two normal alleles or individuals with two harmful alleles. The sickle cell allele provides some resistance to malaria, so individuals with the sickle cell allele are less likely to contract the disease. However, individuals with two copies of the sickle cell allele can develop sickle cell anemia, which is a serious and sometimes fatal condition. Therefore, the higher proportion of heterozygous individuals in these populations is a result of natural selection favoring this genotype in regions where malaria is common.

In Some Human Populations,the Proportion of Individuals Who Are Heterozygous