How many haplotypes are associated with sickle cell anemia?
Five haplotypes are associated with sickle cell anemia. These haplotypes are mainly exhibited in African countries and distributed throughout the continent. Historically, sickle cell anemia haplotypes were first discovered in African countries and usually affect blacks. Furthermore, the locations are not necessarily where they originated from. The four places in Africa where sickle cell mutations were initially discovered are central West Africa (the Benin haplotype), Atlantic West Africa around Zaire and the Congo (the Senegal haplotype), central Cameroon (the Cameroon haplotype), and the equatorial eastern and southern Africa (the Bantu haplotype). The fifth mutation is believed to have originated from either eastern Saudi Arabia or central India (the Arab-Indian haplotype) and later spread to parts of the Middle East. The Benin haplotype is more common and widely spread throughout the northern and western parts of the African continent.
What was the rationale for studying the haplotypes for the sickle cell trait? What goals did the scientists try to achieve?
The rationale behind the study of the haplotypes for the sickle cell trait is that SCA is a heterogeneous disease. Therefore, SCA has its origins from another individual before it inflicts the patient in question. Moreover, a patient’s outcomes are influenced by multiple factors. It becomes necessary to study these factors to come up with a treatment regime that suits the patient’s specific needs. Therefore, this was the goal the scientists were trying to achieve to improve the quality of life and prognosis. Through the study, the scientists would be able to determine the treatment options they intended to use on their patients.
Does haplotype correlate with the severity of sickle cell anemia?
Haplotype correlates with the severity of SCA up to a certain extent. This is usually realized when it comes to clinical observations. Observations have been able to show conclusively that the Senegal and Arab/Indian haplotypes are connected with weak forms of SCA. In comparison, the Bantu haplotype is accompanied by a more rigorous clinical course. Despite this, patients still exhibit differing symptoms which are not associated with their haplotype. Thus, it is the patient’s environment and other allergic differences that influence the severity of SCA. Therefore, in many cases haplotype does not correlate with the severity of SCA.
Using sickle cell anemia as an example, explain what heterozygote advantage is and how positive selection works.
In certain situations, SCA leads to heterozygote advantage. Heterozygote advantage can be described as a situation whereby the heterozygote genome is characterized by a higher relative fitness in comparison to the homozygote dominant. This advantage is usually seen in patients who live in areas with high malaria outbreaks. The consequence of the opposing selection pressures is to save the sickle cell allele within populations in areas where malaria is a significant environmental factor. One advantage of this is that it protects the patient with sickle cell anemia from malaria. Positive selection arises whereby the person with SCA is characterized with improved immunity from infections and easily survives any outbreaks that arise. For instance, in cases of malaria infection, pathogens that cause malaria cannot spend their life cycle in the sickle cells. Thus, the immune system is able to destroy easily the pathogens.