Shenk seems appalled by the idea that the stereotype that African-Americans are better at certain sports (especially running) exists. He emphasizes that while "geneticists and scientists...found that their "secret weapon" was the protein- alpha actinin-3" (101) , this in reality, was not a secret weapon because while 98% of Jamaicans had this protein, so did "80% of Americans, almost 240 million people." (101) He claims that it's "climate, demographics,... and folklore" (101) which have influenced the gene which facilitates the production of this protein to be activated. However, since this gene has been activated over so many generations, is it possible that evolutionary changes within African-Americans have occurred over time relative to the Caucasian or any other population? What physical differences might have manifested themselves to actually make the African-Americans more physically able to have this gene activated (think positive feedback?) or would any at all? Why do Jamaicans still have 18% more of their population proportionally than we do with this gene? Do you think if a Caucasian grew up in the same environment as a Kenyan runner, they could be just as successful? Explain your answer using justification from the book and incorporating the themes of evolution and/or structure and function.
(Michelle Kelrikh, mjkelrikh@gmail.com)
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ReplyDeleteThe ACTN3 gene is not only present in nearly all Jamaicans, but also a comparable majority of Americans and Europeans. Yet, as Shenk states, the Jamaicans are more successful when it comes to sprinting. Looking at the actual genetic code, however, is unlikely to produce real answers to this dilemma. Rather, answer for the continued sprinting superiority in the Jamaican population could lie in the epigenome. Epigenomic traits are “transmitted by mechanisms not directly involving the nucleotide sequence”(Campbell 358). This variation of traits, unrelated one's genotype, occurs in the chromatin packaging that surrounds DNA. Changes in the epigenome have been shown to be able to produce two “very distinct flowers” with the “same genetic code” (158). The effects of that epigenome could just as easily affect the expression of the ACTN3 gene in humans. Additionally, “changes to the epigenome can be inherited” (159), so it is logical that the excellence caused by the varied expression of the ACTN3 gene would be concentrated in certain populations like Jamaicans.
ReplyDeleteThe “epigenome…can be altered by the environment” (159), so there likely is some environmental factor that leads to Jamaican sprinting superiority. It could have been initiated by a lack of motorized transportation in Jamaica relative to more developed places like Europe and America, which would have lead to an increased proportion of the population required to walk or run on a regular basis. Then, since the Jamaican economy has an incredibly low per capita GDP of $9,000, compared to America's $48,100 per capita GDP (https://www.cia.gov/library/publications/the-world-factbook/geos/us.html), and since a lower per capita GDP correlates to a lack of education, individuals individuals of Jamaica, which “based on the achievements of its sprinters...is known...the world, as the home of sprinting”(http://jamaica-gleaner.com/gleaner/20120205/sports/sports32.html ), may only see sprinting as a possibility for success . Due to this, Jamaicans may now strive harder from childhood to become successful sprinters, and this work ethic, as seen in the case of Ted Williams, could also cause variation of overall gene regulation of these Jamaicans to further help them in sprinting. So, both of these environmental stimuli may have resulted in the change in the epigenome affecting the expression of the ACTN3 gene as a whole.Therefore, the GxE interaction that Shenk stresses throughout this book explains for a varied level of expression of the ACTN3 gene, with the perceived effect of Jamaican running superiority.
This relates to the biological theme of evolution, referring to the "descent with modification" of different species from a common ancestor through natural selection. While the divergence within the human species has not caused anything radical like the formation of a new species, the divergence, nonetheless, represents evolution. The Jamaican population, requiring more ACTN3, have evolved to express that gene more frequently, possibly acetylating ACTN3 DNA, to promote the expression of that gene. Seeing as "all organisms...must regulate which genes are expressed" (Campbell 356) and the fact that, as Shenk points out, changes to the epigenome can be inherited, the logical conclusion is that sprinters of Jamaica, being required and encouraged to sprint more often than in America, would generally perform better than other sprinters.
Neil Edat (neil.edat@gmail.com)