For example, in the case of sickle beta thalassemia, the individual has inherited a gene for hemoglobin S. from one parent and a gene for beta-thalassemia from the other. Or, in the instance of SC disease, the individual has inherited a gene for hemoglobin S. from one parent and a gene for hemoglobin C. from the other.

The sickle cell trait in heterozygous carriers confers the resistance to malaria phenotype characterized by a dominant gene (Sickle cell anemia, Wikipedia). Because people with sickle trait were more likely to survive malaria outbreaks in Africa than those with normal hemoglobin, it is believed that sickle hemoglobin evolved as a protection against malaria.

Haplotypes of sickle cell disease are polymorphic restriction endonuclease sites in and around the mutant beta-globin gene Acording to Fields (2000), the existence of haplotypes specific to certain regions of the world suggests that the mutant beta globin gene arose...
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