Question One: What advantage does the sickle cell trait offer to people living in areas where malaria is prevalent?
The sickle cell trait provides protection for people living in a malaria-infected region. Despite its lethal effects on the body’s functionality, the sickle cell trait protects the carrier from malaria. Research hypothesize that the sickle cell trait evolved due to the imperative protection from malaria it provides (Grosse, et al., 2011). To understand the dynamics in the relation, sickle cell protection of malaria, we must understand the major life cycle of malaria. First, the parasite (Plasmodium species) enters the host as sporozoites and replicates in the liver then consumes the hemoglobin in the red blood cells initiating red blood cells to lyse. In defending malaria, during the life cycle, the parasite can be stopped when red blood cells are invaded or as they multiply. As such, having a sickle cell trait will create a protective mechanism during this phase (LaMonte, et al., 2012). Furthermore, research suggests that people with sickle cell trait possess three microRNAs which reduce the replication of P. falciparum replication as well as growth which in turn acts as a way to resist Malaria (Billo, et al., 2012).
Question Two: What have you learned about changes in allele frequencies with and without natural selection? What impact does this have on evolution in populations?
Some factors affect the frequency changes in alleles with or without natural selection. First, I have learned that natural selection allows for passage of alleles that are somehow beneficial. Also, it is a proven fact that mutation increases the frequency of alleles in a particular population. Additionally, non-random relationships or mating might allow individuals of the same genotype to mate as such increasing the alleles. Other factors that affect the frequency of alleles include migration and genetic drift. A frequency change of alleles defines evolution. Darwin did not figure out the dynamics of allele changes, as such as we explain evolution, as a change in genetic make-up, change in the frequency of alleles is the core foundation of the differences in one generation’s characteristics and the other.
Question Four: Why is the sickle cell allele relatively common in parts of Africa but relatively rare in the US?
According to Grosse, et al. ( 2011)studies about sickle cell condition in Africa, it is stipulated that the disease is associated with high child mortality rate. Also, according to our class reading, Africa being termed as a prevalent malaria region as compared to the US, the sickle cell trait evolution being attributed as a vital protection of malaria. As such, it defines the dynamics as to why there are more sickle cells alleles in Africa (7% of its population) than in the US (Makani, Williams, & Marsh, Jul 2013).
Question 4: Why isn’t the sickle cell allele eliminated from human populations entirely?
Sickle cell alleles are recessive alleles, and as such, they can remain in the population for generations in the heterozygous form where the dominant allele masks the recessive allele. For example, the sickle cell allele’s recessive form offers protection from malaria. According to the theory of natural selection, sickle cell allele possesses an advantageous trait of protection. Therefore it would be impossible to eliminate the allele entirely from the population as opposed to deleterious alleles, a plausible possibility (Grosse, et al., 2011).
Billo, M. A., Johnson, E. S., Doumbia, S. O., Poudiougou, B., Sagara, I., Diawara, S. I., & Rice, J. (2012). Sickle cell trait protects against Plasmodium falciparum infection. American Journal of Epidemiology, 176(suppl 7), S175-S185.
Grosse, S. D., Odame, I., Atrash, H. K., Amendah, D. D., Piel, F. B., & Williams, T. N. (2011). Sickle cell disease in Africa: a neglected cause of early childhood mortality. American Journal of Preventive Medicine, 41(6), S398-S405.
LaMonte, G., Philip, N., Reardon, J., Lacsina, J. R., Majoros, W., Chapman, L., & Haystead, T. (2012). Translocation of sickle cell erythrocyte microRNAs into Plasmodium falciparum inhibits parasite translation and contributes to malaria resistance. Cell host & microbe, 12(2), 187-199.
Makani, J., Williams, T. N., & Marsh, K. (Jul 2013, July 18). Sickle cell disease in Africa: burden and research priorities. Annals of Tropical Medicine & Parasitology , 101(1). doi:10.1179/136485907X154638