Estudo da diversidade genética humana em populações nativas e miscigenadas através da utilização de INDELs informativos de ancestralidade localizados no cromossomo 5 e microssatélites tetra-locais do cromossomo Y DYS464 e DYS503

Abstract

In the first chapter of this thesis we evaluated a panel of 31 INDELs with wide variation in allele frequency between Africa and Europe (average = 0.46) in a single chromosomal region, covering 90Mb of the long arm of chromosome 5. First, we genotyped the 31 INDELs in 1045 samples from 52 worldwide populations, distributed in seven geographical regions from the HGDP-CEPH Human Genome Diversity Cell Line Panel. The analysis of molecular variance (AMOVA) showed that, within populations, the difference between individuals is equivalent to approximately 81% of genetic variability, while the difference between geographic regions is about 16%. A graphical representation (multidimensional scaling) of the distance matrix based on Fst distance (Reynolds) with the 52 populations revealed five clear clusters corresponding to the five main geographical regions: Africa, Oceania, East Asia, Americas and Eurasia (Europe and Central Asia, Middle East). Our results corroborate previous studies with widespread chromosomal location. Then, in order to infer the ancestral origin of chromosomal fragments and characterize the admixed pattern of the Brazilian population, we studied the 31 INDELs in 261 unrelated individuals self-classified according to the IBGE as black (n = 104) and whites (n= 157) from São Paulo. Using the parental populations as reference, the probable ancestral origin of each locus was estimated for each chromosome of each Brazilian individual. The results showed that on average, each black Brazilian individual has 27% of the chromosome region analyzed from Europe, 53% of African origin and 19% of Amerindian origin, while for whites Brazilians, these percentages were 60%, 16% and 24% respectively. A significant correlation between the number of loci from the same ancestral origin between the two homologues chromosome 5 of the same individual was found for both black (p <0.000001) and white Brazilians (p <0.000001). One possible explanation for these findings is assortative marriage according to color, but independent of genomic ancestry. Our results showed that the markers used in this study are able to discriminate the three ancestral Brazilian roots and the approach used in the characterization of the Brazilian population at chromosomal level was adequate. In the second chapter of the thesis, two tetralocal Y- linked microsatellites were studied in all samples of men from the CEPH-HGDP Panel. Furthermore, we evaluated the use of allele frequencies of DYS464 in inference of mixing ratios of admixed populations. In our studies of worldwide populations with the DYS464, fourteen different alleles were found with allele lengths varying from 9 to 23 repeats. A total of 175 different genotypes were observed, of which 90 appeared to be continent-specific. The region with the highest percentage of unique genotypes was Africa. Genotype diversity was 0.98 for Europe, 0.97 for Central and East Asia, 0.95 for Africa, 0.94 for Oceania, 0.92 for the Middle East and 0.90 for the Americas. A hierarchical analysis of molecular variance (AMOVA) showed low levels of worldwide genetic structure: 88.42%. The use of allele frequencies of DYS464 to the inference of the mixing proportions in admixed populations showed values that corroborate data found in the literature. The microsatellite DYS503 showed lower allelic pattern diversity in Africa than in most other continents. Our results demonstrated that although DYS464 microsatellite does not permit detailed phylogeographical inferences, it is highly polymorphic and still appears to be an informative tool for evolutionary and admixed population studies. Furthermore, the low diversity of DYS503 is in an unusual result that to be understood should be further studied