In chapter 6, Shenk describes that Jamaican dominance in
sprinting cannot be rooted solely in genes, because their biological “secret weapon”
of the ACTN3 gene, which is found in 98% of Jamaicans, is also found in a 80%
of Americans and 82% of Europeans, yet the latter two groups have not enjoyed
the same sprinting success as have Jamaicans. The ACTN3 gene codes for the
protein alpha-actinin-3, which “drives forceful, speedy muscle contractions”
and assists in exceptional athletic ability (101). Do you think the difference
in athletic ability between Jamaicans and Americans or Europeans is attributed to
Shenk’s argument of GxE, in which different environmental factors that are more
prevalent in Jamaica activate the ACTN3 gene more frequently, therefore
producing more people with the potential to be world class sprinters? Or could
the differences in percentages of a population with the ACTN3 gene reflect the
beginning of an evolutionary adaptation and gene mutations as ACTN3 is slowly becoming
a less frequent allele in the gene pool of certain populations? Relate your response to the gene expression unit
and the theme of evolution.
David Ribot (ribotdavid@gmail.com)
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ReplyDeleteThe ACTN3 gene is present in nearly all Jamaicans and a sizeable majority of Americans and Europeans; yet, as Shenk says, the Jamaicans are more successful when it comes to sprinting. As the Indian newspaper, "The Hindu" points out, "The Jamaican sprinting prowess is all too well-known. Though the country's best had not been entered in the Commonwealth Games here, Lerone Clarke showed that the Jamaican flag would be in the middle when the 100-metre medals ceremony was held, with a 10.12 triumph." (http://www.thehindu.com/sport/athletics/article818489.ece) Looking at the actual genetic code, however, is unlikely to produce real answers – rather, the real reasons for “running superiority” in the Jamaican population lie in the epigenome – the packaging surrounds DNA. Changes in the epigenome have been shown to be enough to cause two “very distinct flowers” with the “same genetic code” (158). The effects of that epigenome on humans could easily affect the expression of the ACTN3 gene. Additionally, “changes to the epigenome can be inherited” (159), so it logically follows that the excellence caused by the varied expression of the ACTN3 gene would be concentrated in certain populations, i.e., Jamaica.
ReplyDeleteThe “epigenome…can be altered by the environment” (159), as Shenk says, so there likely is some environmental factor that leads to Jamaican sprinting superiority – possibly a lack of motorized transportation, which would lead to an increased proportion of the population required to run on a regular basis – that results in the change in the epigenome affecting the expression of the ACTN3 gene. On the other hand, in developed countries, public motorized transportation is readily available to those who require it, so in countries such as America, people are less likely to use the alpha-actinin-3 they would use to gain superiority in these sprints. In both cases, the GxE interactions lead to 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 via natural selection. While the divergence within the human species has not resulted in anything as radical as a new species being generated, the divergence 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 individuals in Jamaica, being required to sprint more often than in America - the Jamaican economy has the 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) The resulting poorer conditions in Jamaica have stimulated greater expression of the ACTN3 gene, which has resulted in the percieved "running superiority" in Jamaica.
Ari Bakke
-Aribakke@gmail.com