Question

• explain, in detail, the relationship between malaria and sickle-cell anemia. Why is having one sickle-cell allele considered a selective advantage? Is this equally beneficial for someone who is homozygous recessive for sickle-cell? Why or why not?

  Note: use specific vocabulary to describe your answers (genotype, homozygous d, homozygous r, natural selection, heterozygous, etc)

Answer 1

Answer:

Sickle cell anemia is a homozygous recessive disease. People who are heterozygote for the allele usually act as carriers. Sickle cell anemia is caused by the single amino acid mutation in the beta chain of hemoglobin. Inheritance of this mutated gene from both parents leads to sickle cell disease and people with this disease have shorter life expectancy. Their blood cells become misshapen and this can block blood flow and people with sickle cell disease are at risk of complications and may die in younger age. Natural selection would normally keep harmful alleles from becoming popular. But in areas where malaria is prevalent, the normal homozygous dominant are more prone to malarial attack. But in heterozygous individuals, the red blood cells are resistant to malaria infection. That means people with the trait are protected from the disease and have an advantage over people without sickle cell trait. So in these areas natural selection go in favour of heterozygous individuals who can survive sickle cell anemia and malaria.