Natural selection for sickle cell allele?

Question

Why does natural selection favor individuals who are heterozgous for the sickle cell allele in certain enviroments?

Answer 1

Please don't fall into thinking that this is evidence of evolution.

It is not. It is an example of a defective mutation and natural selection.

Sickle-cell anaemia is caused by an inherited defect in the instructions which code for the production of haemoglobin, the oxygen-carrying pigment in red blood cells. You will only develop the full-blown, serious disease if both of your parents have the defective gene. If you inherit the defect from only one parent, the healthy gene from the other one will largely enable you to escape the effects of this serious condition.

However, this means you are capable of transmitting the defective gene to your offspring, and it also happens that such carriers are less likely to develop malaria, which is often fatal. Being a carrier of sickle-cell disease without suffering it (heterozygosity is the technical term) is far more common in those areas of the world which are high-risk malaria areas, especially Africa.

This is good evidence that natural selection plays a part in maintaining a higher frequency of this carrier state. If you are resistant to malaria, you are more likely to survive to pass on your genes. Nevertheless, it is a defect, not an increase in complexity or an improvement in function which is being selected for, and having more carriers in the population means that there will be more people suffering from this terrible disease. Demonstrating natural selection does not demonstrate that ‘upward evolution’ is a fact, yet many schoolchildren are taught this as a ‘proof’ of evolution.

http://creationontheweb.com/content/view...

Answer 2

If an individual is heterozygous for the allele, they're still more resistant to malaria, but their hemoglobin isn't totally deformed so it can still bind to oxygen fairly efficiently. At least that's what I remember, anyways.

Answer 3

Sickle Cell helps deter malaria which is common in Africa.

Answer 4

This has to do with malaria. It is good to be heterozygous for sickle cell anemia, because not all of the blood cells will be deformed. This means you can live your life without the problems that sickle cell has. But because you have one gene for sickle cell, you will also be resistant to malaria. This is especially good in areas where malaria is very present. That's why sickle cell anemia is most often in areas like Africa and that's why sickle cell anemia is selected for in those areas, unlike here, where it is pretty uncommon.