Gabriela Berardi

Male lineages in South American native groups: evidence of M19 traveling south.

With this study, we aimed to determine the different male ancestral components of two Native American communities from Argentina, namely Toba and Colla. The analysis of 27 Y-chromosome SNPs allowed us to identify seven different haplogroups in both samples. Chromosomes carrying the M3 mutation, which typically defines the Native American haplogroup Q1a3a, were seen most frequently in the Toba community (90%). Conversely, Q1a3a was represented in 34% of the Colla Y-chromosomes, whereas haplogroup R1b1, the main representative of western European populations, exhibited the highest frequency in this population (41%). Different M3 sublineages in the Toba community could be identified by observing point mutations at both DYS385 and M19 loci. A microvariant at DYS385, named 16.1, has been characterized, which helps to further subdivide Q1a3a. It is the first time the M19 mutated allele is described in a population from Argentina. This finding supports the old age of the lineages carrying the M19 mutation, but it contradicts the previous hypothesis that the M19 mutated allele is confined to only two Equatorial-Tucano population groups from the north region of South America. The detection of M19 further south than previously thought allows questioning of the hypothesis that this lineage serves as an example of isolation after colonization. This observation also affirms the strong genetic drift to which Native Americans have been subjected. Moreover, our study illustrates a heterogeneous contribution of Europeans to these populations and supports previous studies showing that most Native American groups were subjected to European admixture that primarily involved immigrant men.

Evaluating Methods to Correct for Population Stratification when Estimating Paternity Indexes

The statistical interpretation of the forensic genetic evidence requires the use of allelic frequency estimates in the reference population for the studied markers. Differences in the genetic make up of the populations can be reflected in statistically different allelic frequency distributions. One can easily figure out that collecting such information for any given population is not always possible. Therefore, alternative approaches are needed in these cases in order to compensate for the lack of information. A number of statistics have been proposed to control for population stratification in paternity testing and forensic casework, Fst correction being the only one recommended by the forensic community. In this study we aimed to evaluate the performance of Fst to correct for population stratification in forensics. By way of simulations, we first tested the dependence of Fst on the relative sizes of the sub-populations, and second, we measured the effect of the Fst corrections on the Paternity Index (PI) values compared to the ones obtained when using the local reference database. The results provide clear-cut evidence that (i) Fst values are strongly dependent on the sampling scheme, and therefore, for most situations it would be almost impossible to estimate real values of Fst; and (ii) Fst corrections might unfairly correct PI values for stratification, suggesting the use of local databases whenever possible to estimate the frequencies of genetic profiles and PI values.

STR data for PowerPlex®16 System from Buenos Aires population, Argentina

Allele frequencies for the 15 autosomic STR loci included in the PowerPlex 16 System kit (Promega Corp.) were estimated from a sample of 143 unrelated individuals living in Capital Federal and in Buenos Aires Metropolitan Area, Argentina. Population showed to be in HWE.

A comprehensive Y-STR portrait of Argentinean populations

A study of 23 Y-STRs was conducted in 257 individuals living in urban areas from eight Argentinean provinces. The data were meta-analyzed together with 364 profiles obtained from the literature that represent other five provinces. A total of 255 different haplotypes were observed (253 singletons). Genetic structure estimated from analysis of molecular variance (AMOVA) and exploring different grouping scenarios, yielded high within population variance. Not surprisingly, analyses of genetic distances with respect to main ancestral continental populations indicated Argentinean haplotypes to be closely related to European ones. Overall, these results provide a quite complete picture of the patterns of Y chromosome variation in Argentina, notably contributing to increase the previous national database, and consequently allowing a better estimation of parameters of interest in forensic casework and parentage testing.

STR data for PowerPlex®16 System from Neuquen population, SW Argentina

Allele frequencies for the 15 autosomic STR loci included in the PowerPlex 16 System kit (Promega) were estimated from a sample of 111 unrelated individuals living in Neuquen province, southwest of Argentina. Population showed to be in HWE.

Charting the Y-chromosome ancestry of present-day Argentinean Mennonites

Old Order Mennonite communities initially arose in Northern Europe (centered in the Netherlands) and derived from the Anabaptist movement of the 16th century. Mennonites migrated to the New World in the early 18th century, first to North America, and more recently to Mesoamerica and South America. We analyzed Y-chromosome short tandem repeats (STRs) and single nucleotide polymorphisms in males from a community of Mennonites, ‘La Nueva Esperanza’, which arrived to Argentina in 1985 from colonies in Bolivia and Mexico. Molecular diversity indices coupled with demographic simulations show that Mennonites have a reduced variability when compared with local Argentinean populations and 69 European population samples. Mennonite Y-STR haplotypes were mainly observed in Central Europe. In agreement, multidimensional scaling analyses based on RST genetic distances indicate that Mennonite Y-chromosomes are closely related to Central/Northern Europeans (the Netherlands, Switzerland and Denmark). In addition, statistical inferences made on the most likely geographic origin of Y-chromosome haplotypes point more specifically to the Netherlands as the populations that best represent the majority of the Mennonite Y-chromosomes. Overall, Y-chromosome variation of Mennonites shows the signatures of moderate reduction of variability when compared with source populations, which is in good agreement with their lifestyle in small endogamous demes. These genetic singularities could also help to understand disease conditions that are more prevalent among Mennonites.

Species identification in forensic samples using the SPInDel approach: A GHEP-ISFG inter-laboratory collaborative exercise

DNA is a powerful tool available for forensic investigations requiring identification of species. However, it is necessary to develop and validate methods able to produce results in degraded and or low quality DNA samples with the high standards obligatory in forensic research. Here, we describe a voluntary collaborative exercise to test the recently developed Species Identification by Insertions/Deletions (SPInDel) method. The SPInDel kit allows the identification of species by the generation of numeric profiles combining the lengths of six mitochondrial ribosomal RNA (rRNA) gene regions amplified in a single reaction followed by capillary electrophoresis. The exercise was organized during 2014 by a Working Commission of the Spanish and Portuguese-Speaking Working Group of the International Society for Forensic Genetics (GHEP-ISFG), created in 2013. The 24 participating laboratories from 10 countries were asked to identify the species in 11 DNA samples from previous GHEP-ISFG proficiency tests using a SPInDel primer mix and control samples of the 10 target species. A computer software was also provided to the participants to assist the analyses of the results. All samples were correctly identified by 22 of the 24 laboratories, including samples with low amounts of DNA (hair shafts) and mixtures of saliva and blood. Correct species identifications were obtained in 238 of the 241 (98.8%) reported SPInDel profiles. Two laboratories were responsible for the three cases of misclassifications. The SPInDel was efficient in the identification of species in mixtures considering that only a single laboratory failed to detect a mixture in one sample. This result suggests that SPInDel is a valid method for mixture analyses without the need for DNA sequencing, with the advantage of identifying more than one species in a single reaction. The low frequency of wrong (5.0%) and missing (2.1%) alleles did not interfere with the correct species identification, which demonstrated the advantage of using a method based on the analysis of multiple loci. Overall, the SPInDel method was easily implemented by laboratories using different genotyping platforms, the interpretation of results was straightforward and the SPInDel software was used without any problems. The results of this collaborative exercise indicate that the SPInDel method can be applied successfully in forensic casework investigations.

Analysis of uni and bi-parental markers in mixture samples: Lessons from the 22nd GHEP-ISFG Intercomparison Exercise

Since 1992, the Spanish and Portuguese-Speaking Working Group of the ISFG (GHEP-ISFG) has been organizing annual Intercomparison Exercises (IEs) coordinated by the Quality Service at the National Institute of Toxicology and Forensic Sciences (INTCF) from Madrid, aiming to provide proficiency tests for forensic DNA laboratories. Each annual exercise comprises a Basic (recently accredited under ISO/IEC 17043: 2010) and an Advanced Level, both including a kinship and a forensic module. Here, we show the results for both autosomal and sex-chromosomal STRs, and for mitochondrial DNA (mtDNA) in two samples included in the forensic modules, namely a mixture 2:1 (v/v) saliva/blood (M4) and a mixture 4:1 (v/v) saliva/semen (M8) out of the five items provided in the 2014 GHEP-ISFG IE. Discrepancies, other than typos or nomenclature errors (over the total allele calls), represented 6.5% (M4) and 4.7% (M8) for autosomal STRs, 15.4% (M4) and 7.8% (M8) for X-STRs, and 1.2% (M4) and 0.0% (M8) for Y-STRs. Drop-out and drop-in alleles were the main cause of errors, with laboratories using different criteria regarding inclusion of minor peaks and stutter bands. Commonly used commercial kits yielded different results for a micro-variant detected at locus D12S391. In addition, the analysis of electropherograms revealed that the proportions of the contributors detected in the mixtures varied among the participants. In regards to mtDNA analysis, besides important discrepancies in reporting heteroplasmies, there was no agreement for the results of sample M4. Thus, while some laboratories documented a single control region haplotype, a few reported unexpected profiles (suggesting contamination problems). For M8, most laboratories detected only the haplotype corresponding to the saliva. Although the GHEP-ISFG has already a large experience in IEs, the present multi-centric study revealed challenges that still exist related to DNA mixtures interpretation. Overall, the results emphasize the need for further research and training actions in order to improve the analysis of mixtures among the forensic practitioners.

Genomic continuity of Argentinean Mennonites

Mennonites are Anabaptist communities that originated in Central Europe about 500 years ago. They initially migrated to different European countries, and in the early 18th century they established their first communities in North America, from where they moved to other American regions. We aimed to analyze an Argentinean Mennonite congregation from a genome-wide perspective by way of investigating >580.000 autosomal SNPs. Several analyses show that Argentinean Mennonites have European ancestry without signatures of admixture with other non-European American populations. Among the worldwide datasets used for population comparison, the CEU, which is the best-subrogated Central European population existing in The 1000 Genome Project, is the dataset showing the closest genome affinity to the Mennonites. When compared to other European population samples, the Mennonites show higher inbreeding coefficient values. Argentinean Mennonites show signatures of genetic continuity with no evidence of admixture with Americans of Native American or sub-Saharan African ancestry. Their genome indicates the existence of an increased endogamy compared to other Europeans most likely mirroring their lifestyle that involve small communities and historical consanguineous marriages.

Data analysis of 10 STR loci in a population in the province of Neuquen, Argentina

Abstract Ten Short Tandem Repeat (STR) loci, CSF1PO, TPOX, THO1, D12S1090, D3S1744, D18S849, FGA, D7S820, D1S533 and D9S304, were analyzed in a population geographically located at the foot of the Andes Range in the province of Neuquen, southwestern Argentina. Allele frequencies and paternity and forensic parameters (power of exclusion, matching probability, and power of discrimination) were calculated for all 10 STR loci. The population was analyzed for Hardy-Weinberg equilibrium (HWE) and allelic and gene frequencies were compared to those observed in the Buenos Aires population. Results indicate that the population was in HWE for these 10 STR loci. Significant differences between allele and genotype frequencies were found for the D7S820 locus (gene and genotypic differentiation test) when compared with data of the Buenos Aires population. These data indicate that the allele frequency estimations can be used to reliably calculate likelihood ratios for paternity and forensic DNA casework.