Sickle Cellular Adaptation

Over the generations, ancestors evolved different allele frequencies due to recurring natural selection. In fact, natural selection and mutation were considered the main hypotheses for the sickle gene cell. However, those hypotheses limit in explaining the entirety for the frequency of the HbS allele in human populations around the globe. The complex relationship between the HbS allele frequencies and the level of malaria prevalence support the malaria hypothesis at a global scale and further demonstrate why adaptation or natural selection alone cannot be the factor in explaining allele frequencies. According to Piel et. al. (2010), HbS, known as the sickle hemoglobin, is “a structural variant of normal adult hemoglobin” (p. 2). Piet et al. (2010) recognized several limitations from the past studies such as “biased HbS allele frequency estimates and population samples” (p.2). Before going into the comprehensive geographical maps and data, they presented how human populations showed responses to malaria based on multiple genetic factors. Malaria and hemoglobin adaptation seems to be an important relationship in explaining genetic disorders such as beta thalassemia and the sickle cell disease, which is caused by mutations in the HBB gene (Genetics Home Reference: HBB, 2015). A single mutation on the Hb gene not only produces sickle blood cells but also impairs hemoglobin functionality. Furthermore, A homozygote, which is when you inherit the disease allele from both parents, is at a higher risk as to a heterozygote that is marked by malaria resistance in carriers (Piel et. al., 2010, p.2). This relationship with the HbS and malaria is evident in Africa based on our class activity and from the genetic perspective. Based on the hypothesis, it is more likely that Central West Africa became the source for the HbS haplotype. Because of the HbS mutation, I concluded that introns in Central Africa had more diversity and variation in their natural selection, which makes it a strong factor in malaria resistance. This is why SNP haplotypes connected to the HbS allele are most common in regions in Africa. The HbS haplotype that exists in Eurasia might be due to both cultural and environmental factors such as Islamic expansion or the West African labor in the Middle East. Thus, we can see that there is a wider geographic spread of allele and mutations spreading to other regions outside of West Africa. Piel et al. indicated both the genetic side and the level of malaria endemicity at a global level and showed the distribution of sickle cell genes in regions where there are high prevalence rates. Yet, Livingstone’s study further supports the malaria hypothesis in the Central and West Africa by presenting …show more content…
Livingstone presents the linguistic evidence for migration patterns over generations, which gives more support on the malaria hypothesis. Because of the common ancestries, languages are genetically related and possess different conditions for each groups based on their geographic regions. For example, Livingstone (1958) noted that Gambia and Sierra Leone has the highest frequencies of the sickle gene cell (p. 546). The Mande people moved in large numbers and seemed to introduce the particular gene into parts of Africa (Livingstone, 1958, p. 547). This large-scale migration led to higher frequencies of the sickle cell traits, which lends evidence about the HbS allele frequency variation. The linguistic evidence supports the West African HbS allele frequency variation because the migration pattern shows the spread of the selective advantage of the sickle cell gene. The environmental variation matters a lot especially for this case as language gives significant biological influence on the human populations. In addition, cultural development based on archeological evidence further explains how various adoption and geographic spread of agriculture technology caused exposure of high frequencies in human populations. The rice cultivation exemplifies gene flow, as it was responsible for the spread of the sickle cell gene in West Africa. According to Livingstone (1958), the relationship between the spread of the agriculture by diffusion and its frequencies exposed human populations to the parasites (p. 553). As human populations grew over time, the environmental change resulted in the “adaptation of several species of the Anopheles gambiae to human habitations and the adaptation of many parasites to man as their host” (Livingstone, 1958, p. 556). The adaptation is probably from the agricultural technology