| Summary: | Elite athletic performance is widely acknowledged to result from the exposure of a favourable genetic endowment to a favourable combination of environmental factors including culture, diet, training regime and socioeconomic status. Athletes from West African descendant populations in North America and Western Europe have long been prominent in elite sprint running, constituting 63% of the top 100 performers in each sprint discipline, outperforming athletes from Europe (23%), West Africa (8%) and the rest of the world (6%). These members of the West African diaspora are genetically admixed, resulting in detectable levels of both African and European ancestry because of gene flow between African slaves and Europeans during chattel slavery in the 16th to 19th centuries. The overall aim of this thesis was to investigate the effect that ancestral genetic composition may have had on the likelihood of becoming a top-class sprint athlete amongst samples of African-Americans and Jamaicans. It was hoped that these findings would add to the existing research in attempting to understand the unique combination of factors that produce elite sprint athletes. Ancestrally informative genetic data from elite African-American and Jamaican sprint athletes and ethnically-matched controls were used to explore how genetic ancestry affects sprint athlete status in these populations. These data are also vital when investigating the putative origins of an admixed population, and relatively little research has investigated the genetic ancestry of modern Jamaicans when compared to African-Americans. To bring the two groups to comparable levels of insight, the population history of the Jamaican people was estimated by comparing the observed matrilineal gene pool to the gene pools of known source regions of Africa. By simulating a stable population with the observed population dynamics from slave-era Jamaica, it was possible to draw conclusions about selection acting on the Jamaican slave population from the colonisation of the island by England in 1655 until the abolition of the slave trade in 1807. In addition to the Jamaican maternal lineages already genotyped, paternal lineages in both African-Americans and Jamaicans, as well as maternal lineages in African-Americans were genotyped to assess any association these lineages had with elite sprint athlete status. These lineages were also compared between the cohorts to assess any differences in lineage composition across both groups of athletes and controls. Finally, locus-specific genetic ancestry was calculated to map loci associated with elite athlete status to regions of the genome with a greater amount of African or European ancestry than would be expected under the null hypothesis of no association with ancestry. Assuming a difference in the likelihood of sprint athletes originating from either Africa or Europe, detected associations between locus-specific ancestry and sprint status may indicate specific genomic regions of interest. The main findings of this thesis are: a) Modern Jamaicans are mostly descended from slaves originating from the Gold Coast of Africa, despite large influxes of slaves from the Bight of Biafra and West-central Africa before the end of the slave trade. b) There appears to have been selective pressure acting on the slave population of Jamaica. Differences between the presumptive origins of the observed lineages and the outcome of the stable population model suggested varying levels of mortality and fecundity within the slave population, consistent with earlier ethnographic and linguistic studies. c) The distribution of maternal lineages in the African-American athletes were significantly different from that of African-American controls. Maternal lineage distributions between Jamaican athletes and Jamaican controls were not significantly different. There was insufficient statistical power to infer any differences between the paternal lineages of African-American athletes and controls or the Jamaican athletes and controls. This suggests that either maternal ancestry may be a factor in elite sprint athlete status for African-Americans or it could simply be a false positive, inherent to the methodology used. Jamaican maternal lineages are homogeneous with regards to elite sprint athlete status. There was insufficient statistical power to arrive at similar conclusions regarding the paternal lineages of athletes and controls in either group. d) The maternal lineages of African-American athletes and Jamaican athletes were significantly different, although there was insufficient statistical power to determine if there were any differences between the paternal lineages of African-American athletes and Jamaican athletes. This suggests that the same maternal lineage distribution is not associated with sprint athlete status in the two populations, while there is insufficient evidence to make a similar claim regarding paternal lineages. e) The maternal lineages of African-American controls and Jamaican controls were also significantly different, although there was insufficient statistical power to conclude whether significant difference exists in the paternal lineages of African-American controls and Jamaican controls. These results suggest that there is some evidence that the population histories of African-Americans and Jamaicans are significantly different despite the lack of evidence from the paternal lineages. f) The proportion of genome-wide African ancestry did not differ significantly between either African-American athletes and controls or Jamaican athletes and controls. This suggests that environmental factors typically associated with higher levels of African ancestry in these populations (e.g. lower socioeconomic status, diminished access to healthcare) are not directly linked with elite athlete status. g) The estimated number of generations since admixture occurred did not differ significantly between athletes and controls for either African-Americans or Jamaicans. This suggests that athletes were not more likely than controls to have had European ancestors in the recent past, thereby potentially having greater access to resources. h) Admixture mapping was used to detect an enrichment of European ancestry at chromosome 4q13.1 significantly associated with athlete status in African-Americans. There were no significant loci associated with athlete status in Jamaicans. This suggests that the regions of the genome influencing sprint athlete status may be different in the two populations, although there was insufficient statistical power to draw any meaningful conclusions from the Jamaican data. This thesis has potential implications for future work not only explaining the disproportionate success of West African descendant sprint athletes but also for advancing the basic understanding of the genetic influences on the limits of human performance.
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