Population Structure of a Remnant Quilombo Community: An Analysis of the Inbreeding and Ethnic Admixture

Abstract

The histories and oral traditions identify rural communities them as quilombos and that are currently denominated quilombo remnants in Brazil. The formation of these communities was usually carried out by a small number of individuals who remained isolated for generations. This study is an analysis of the effects of inbreeding and ethnic admixture in the remaining quilombo community Tucum in the South-Center region of the State of Bahia, in Brazil. The inbreeding values were obtained through inbreeding coefficients and genealogical database. The admixture analysis was conducted by phenotypic and cultural index. Other demographic genetic parameters were evaluated in the search for the better understanding of the population structure. A total of 489 individuals were analyzed for effective population size (Nef), inbreeding coefficient expected (O), inbreeding coefficient (F) and mean inbreeding coefficient (F) resulting in 384, 0, 0.144, 0.0086, respectively. The community presents 20.64% of consanguineous marriages and an inbreeding coefficient (r) of 0.288. These data are larger than those found in the total Brazilian population and to other traditional communities analyzed in the country. The admixture analysis revealed a Negroid Phenotypic Index (NPI) of 0.60 and the Negroid Cultural Index (NCI) of 0.33, lower than that found in other remnants. The isolation index (i) helps to understand this pattern of population structure, and the community studied was not a genetic isolate (i = 22.4) demonstrating a large migratory flow. Based on the data presented, it is possible to conclude that the community is not a genetic isolate, transcending the initial implications of the founding effect. However, the high migration does not prevent inbreeding and high rates of consanguineous marriages, influenced by cultural ethnic characters, which may change evolutionary mechanisms, as genetic drift, alleles fixation, natural selection (for preferential selection) and an increase in genetic diseases.