While individuals that are homozygous for the sickle cell gene will die, being heterozygous for sickle cell gives you a slight resistance to malaria. This allows the gene for sickle cell to remain so prevalent within an area where malaria is prevalent.
“Sickle-cell disease, usually presenting in childhood, occurs more commonly in people (or their descendants) from parts of tropical and sub-tropical regions where malaria is or was common. One-third of all aboriginal inhabitants of Sub-Saharan Africa carry the gene[2] because in areas where malaria is common, there is a survival value in carrying only a single sickle-cell gene (sickle cell trait).[3] Those with only one of the two alleles of the sickle-cell disease are more resistant to malaria, since the infestation of the malaria plasmodium is halted by the sickling of the cells which it infests.”
Individuals that are carriers for the disease, that is they are heterozygous for the disease, seem to have a resistance to malaria due to shape of their red blood cells. This does not affect them enough to cause them to be sick from the sickle cell and increases their survival against malaria.
Those that are heterozygous where malaria occurs are more likely to survive and pass on the genes for sickle cell than those that do not carry the gene. Therefore, the heterozygous condition is naturally selected for, and the allelic frequency for sickle cell would increase.
Those that are homozygous for sickle cell would not gain enough benefit from the malaria resistance to counter the effects of the disease itself so the disease is still selected against in its homozygous condition.
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While individuals that are homozygous for the sickle cell gene will die, being heterozygous for sickle cell gives you a slight resistance to malaria. This allows the gene for sickle cell to remain so prevalent within an area where malaria is prevalent.
“Sickle-cell disease, usually presenting in childhood, occurs more commonly in people (or their descendants) from parts of tropical and sub-tropical regions where malaria is or was common. One-third of all aboriginal inhabitants of Sub-Saharan Africa carry the gene[2] because in areas where malaria is common, there is a survival value in carrying only a single sickle-cell gene (sickle cell trait).[3] Those with only one of the two alleles of the sickle-cell disease are more resistant to malaria, since the infestation of the malaria plasmodium is halted by the sickling of the cells which it infests.”
Individuals that are carriers for the disease, that is they are heterozygous for the disease, seem to have a resistance to malaria due to shape of their red blood cells. This does not affect them enough to cause them to be sick from the sickle cell and increases their survival against malaria.
Those that are heterozygous where malaria occurs are more likely to survive and pass on the genes for sickle cell than those that do not carry the gene. Therefore, the heterozygous condition is naturally selected for, and the allelic frequency for sickle cell would increase.
Those that are homozygous for sickle cell would not gain enough benefit from the malaria resistance to counter the effects of the disease itself so the disease is still selected against in its homozygous condition.