Unequal contributions of male and female gene pools from parental populations in the African descendants of the city of Melo, Uruguay

Abstract

In admixed populations, genetic contributions from males and females of specific parental populations can be of different proportions due to past directional mating during the process of genetic admixture. In this research paper, we provide evidence of such male- and female-specific differential admixture components of African, European, and American Indian origin in an admixed population from the city of Melo, in the northeastern region of Uruguay. From data on 11 autosomal markers from a sample of 41 individuals of mixed African descent, we estimated 47% African, 38% European, and 15% Amerindian contributions. In contrast, 6 mtDNA site-specific polymorphic markers showed that the mtDNA genome of these individuals was 52% African, 19% European, and 29% Amerindian, while from 3 Y-specific polymorphic sites, we estimated 30% African, 64% European, and 6% Amerindian contributions. We argue that this heterogeneity of admixture estimates results from disproportionate unions of European males with African and American Indian females from which this mixed African population was formed. Also, we argue that the asymmetry of the admixture estimates from the three sets of markers (autosomal, mtDNA, and Y-linked) is a result of the changes in the direction of mating during the history of the population. Implications of such evidence of directional mating are discussed, indicating the need of further demographic data for a quantitative assessment of the impact of directional mating on genetic structure of admixed populations.

alpha-thalassemia, HbS, and beta-globin gene cluster haplotypes in two Afro-Uruguayan sub-populations from northern and southern Uruguay

“…For example, Afro-Amazonian populations, like Ganga in Venezuela and Curiau in Brazil, show 76% and 73.6% of African genetic contribution, respectively, whereas the corresponding HbS carrier frequencies amount to 4.8% and 8.4%, respectively (Castro de Guerra, 1993;. In an Afro-Uruguayan population from the Northeast with similar characteristics to our study population, the African genetic contribution was estimated as being 50% (Sans et al, 2002). The inconsistency between the African genetic contribution and the HbS carrier frequency may be attributed to microevolutionary factors such as genetic drift and/or founder effects, and/or to differences in the origin of the slaves brought to Uruguay.…”

“…Despite the limited sample size of our study, the significant difference in frequency (0.292 vs. 0.036, p = 0.016) between the southern and northern regions is worthy of note. This difference may be explained by the greater contribution of genes from Native American populations to the gene pool of the northern population (Sans et al, 1997(Sans et al, , 2002. Furthermore, the European contribution in the northern region is predominantly of Spanish and Portuguese origin, and in these countries the frequency of a-thalassemias is comparatively lower that in other Mediterranean countries (Villegas et al, 2001).…”

“…For example, Sans et al (1997), using protein and blood group markers, showed that in Montevideo the contribution of populations of European, African, and Native American origin were 92%, 7%, and 1%, respectively, while in the northeastern city of Tacuarembó, the respective contributions were 65%, 15%, and 20%. Among self-identified Afro-Uruguayans from Melo, the contribution of African genes determined by autosomal loci markers was around 50% (Sans et al, 2002).…”

The Genetic Diversity of the Americas

“…A dramatic early example of this approach was provided by the population of Antioquia in Colombia, where ~90% of Y chromosome lineages are of European origin, whereas ~90% of mtDNA lineages are Native American, indicating that the foundation of the population from this province overwhelmingly involved European men and native women, although this is not specifically recorded in historical documents (12,25,26). Similar analyses of other Ibero-American populations have often documented paternal lineages as mainly European, whereas maternal lineages are predominantly Native American or African (3,7,28,41,55,60,88). Y chromosome and mtDNA analyses have more recently been enriched by the use of X chromosome and autosomal data showing that the proportion of European ancestry estimated for the X chromosome is lower than that for the autosomes, as expected from the fact that women contribute two X chromosomes to the next generation, whereas men only contribute one (12,108).…”

Dominant Contribution of Northern Chinese to the Paternal Genetic Structure of Chaoshanese in South China

“…Population admixture, one of the major themes in the study of human evolution, is being delineated for a number of populations, on different continents, by analyzing genetic variations using various genetic markers such as single nucleotide polymorphisms (SNP), mitochondrial DNA (mtDNA), and autosomal-and Y-chromosomal STRs (Y-STR) (Carvajal-Carmona et al 2000;Benedetto et al 2001;Gresham et al 2001;Helgason et al 2001;Sans et al 2002;Bosch et al 2003;Wen et al 2004a, b;Kayser et al 2008). Knowledge of population admixture enables an understanding of the historic, genetic, and evolutionary aspects of the relevant populations.…”