Explain how the sickle-cell allele can be adaptive.

Question

blues · Answer

The sickle cell allele is incompletely dominant. That is, individuals who are heterozygous for the trait show a phenotype (have red blood cells) which are half way between entirely sickle shaped and normally shaped.

It turns out that it is much harder for the malaria plasmodium to enter partially sickle shaped red blood cells. It is adapative (for the people with the incompletely dominant phenotype) because they don't get malaria and adaptive on a population level because it reduces the number of people who could potentially transmit the disease to every one else.

Clear?

anonymous · Answer

Sickle cell anemia could be adaptive in the way that it offers protection against malaria. Sickle cell anemia is dominant genetic disorder whereas if you inherit it from both parents (AA alleles) then you die early in life because your blood cells are unable to carry the required amount of oxygen. However if you only inherit it from one parent (Aa alleles), then only part of your blood cells shows the characteristic sickle shape while the other part is fully functional. We have not yet discovered the reason behind this, but it plays a part in protecting against the malaria parasite.

anonymous · Answer

It is not only harder for malaria plasmodium to enter partially sickle shaped RBC, it also seems to protect the parakrin normallly shaped erytrocytes from being infected.