Marcadores Inserção/Deleção (Indel): estudo de ancestralidade e identificação humana na população brasileira

Abstract

Indels are length polymorphisms created by the insertion or deletion of one or more nucleotides in a DNA sequence. This type of genetic marker is potentially very useful for forensic and population genetic applications because it combines some desirable SNP features, such as the possibility of being analyzed in small fragments (less than 250bp), and low mutation rate, and in the same way as for the STRs it is easily genotyped in a single PCR followed by capillary electrophoresis detection of the amplified fragments. In order to evaluate the efficiency of Indels in forensic applications, and clarify some details on the formation of different Brazilian populations through genetic data, population samples from different Brazilian States were genotyped through two Indel multiplex systems. The first (Indelplex-HID) has been optimized for Human Identification (HID), and includes a group of 38 Indel markers selected by presenting similarly high values of genetic diversity within the main continental populations. The second (46-AI-indels) was selected for studies of ancestry, and it is composed by a set of 46 ancestry informative markers (AIMs). The latter, unlike the first one, includes markers with high divergence in allele frequencies among populations. In a first stage, the multiplex HID was used to study a population sample of Rio de Janeiro and a population sample of Terena Amerindians. Allele frequency databases were built for these two population samples. Allele frequency values were used in statistical comparisons, and to calculate relevant kinship and identification parameters. The cumulative discrimination power for the 38 loci in the population from Rio de Janeiro was 0.9999999999999990, and for the Terena Indians it was 0.9999999999997, demonstrating the utility of this system in a heterogeneous population like the Brazilian. The effectiveness of the indelplex-HID was also revealed to be high in low template samples that have been analyzed, which were previously selected from forensic cases, showing better results than STR markers in terms of number of genotyped loci and amplification quality. In the second stage, the multiplex 46-AI-indels was used to assess the ancestry makeup of different States of Brazil, since it allows the identification of differences among allele frequencies in geographically separated population groups. Most of the populations analyzed showed high European heritage. The populations from Rio de Janeiro, Pernambuco, Mato Grosso do Sul, Manaus, Alagoas, Minas Gerais and São Paulo presented about 50% European ancestry, while in Espirito Santo and south of Brazil the frequency of European ancestry was about 70%. In General, the Amerindian and African contributions varied somewhat according to the region. Santa Isabel do Rio Negro and Terena (indicated as Ameridians-descendants) in fact showed mostly Amerindian ancestry (>70%). The results of AIMs typing are in close agreement with the historical records and other genetic studies on the formation of Brazilian population. The loci of the HID system were highly informative, and constitute an important tool in human identification and kinship studies.