PIMA: A population informative multiplex for the Americas.

We describe an ancestry-informative autosomal SNP multiplex designed to be a small-scale, flexible panel that can complement uniparental markers in assessing the American variability (i.e. pre-Colombian) found in contemporary indigenous American populations. This study centered on choosing SNPs with the specific characteristics of: 1) extreme allele frequency differences between indigenous Americans and the African, European and East Asian population groups that contribute to present-day population variation in the Americas; 2) high informativeness-for-assignment In values; and 3) well-spaced genomic distribution and chromosomal separation from existing small-scale forensic ancestry marker sets. The resulting capillary electrophoresis SNaPshot single base extension test was named: PIMA (Population Informative Multiplex for the Americas), comprising 26 autosomal SNPs, a single X-chromosome SNP plus the amelogenin sex marker adapted for SNaPshot. PIMA complements the established 34plex forensic ancestry panel to provide a powerful and simple tool for the analysis of American populations, including those with admixed histories, commonly encountered in America. Comparing the results obtained with the combined marker panels of PIMA and 34plex to SNP data from a much larger ancestry panel allowed us to gauge their relative efficiency. PIMA+34plex gives equivalent power to the 314-SNP 'LACE' genomic ancestry control panel, while requiring a much smaller genotyping effort. The ancestry profiles and genetic structure of 22 populations spread across the American continent were estimated using PIMA+34plex data, and those estimates were contrasted with information provided by uniparental markers (mtDNA and Y-chromosome loci) for a small set of admixed individuals from Venezuela. Our results indicate that an American genetic component is efficiently detected in contemporary American populations using a small set of ancestry informative SNPs, and these co-ancestry estimates are consistent with the known history and demography of the Americas. The small scale and high population differentiation power of PIMA, particularly when combined with 34plex, provides a practical and powerful tool for genetic studies of American populations as well as forensic DNA analyses.

Exploring iris colour prediction and ancestry inference in admixed populations of South America.

New DNA-based predictive tests for physical characteristics and inference of ancestry are highly informative tools that are being increasingly used in forensic genetic analysis. Two eye colour prediction models: a Bayesian classifier - Snipper and a multinomial logistic regression (MLR) system for the Irisplex assay, have been described for the analysis of unadmixed European populations. Since multiple SNPs in combination contribute in varying degrees to eye colour predictability in Europeans, it is likely that these predictive tests will perform in different ways amongst admixed populations that have European co-ancestry, compared to unadmixed Europeans. In this study we examined 99 individuals from two admixed South American populations comparing eye colour versus ancestry in order to reveal a direct correlation of light eye colour phenotypes with European co-ancestry in admixed individuals. Additionally, eye colour prediction following six prediction models, using varying numbers of SNPs and based on Snipper and MLR, were applied to the study populations. Furthermore, patterns of eye colour prediction have been inferred for a set of publicly available admixed and globally distributed populations from the HGDP-CEPH panel and 1000 Genomes databases with a special emphasis on admixed American populations similar to those of the study samples.

SNP variation with latitude: Analysis of the SNPforID 52-plex markers in north, mid-region and south Chilean populations.

Chile is a disproportionately long and narrow country defined by the southern Andes and Pacific coastline where a level of genetic sub-structure resulting from distances of several thousand kilometers might be expected across the most distantly separated regions. Although STR databases created for the Chilean Legal Medical Service indicate an absence of sub-structure, such a characteristic requires further exploration when introducing additional forensic markers. Notably, Single Nucleotide Polymorphisms (SNPs) have a much lower mutation rate than STRs and can show more stable distributions of genetic variation if population movement is restricted. In this study we evaluated 451 Chilean urban samples from the North, North-Central, Central, South-Central and South regions of Chile for the 52 SNPs of the SNPforID forensic identification panel to explore the underlying genetic structure of Chilean populations. Results reveal similar genetic distances between groups suggesting a single SNP database for the whole of Chile is appropriate. To further understand the genetic composition of Chilean populations that comprise the bulk of individuals with both European and Native American ancestries, ancestral membership proportions were evaluated and pairwise comparisons to other American populations were made.

Analysis of the SNPforID 52-plex markers in four Native American populations from Venezuela.

The SNPforID 52-plex single nucleotide polymorphisms (SNPs) were analyzed in four native Venezuelan populations: Bari, Pemon, Panare and Warao. None of the population-locus combinations showed significant departure from Hardy-Weinberg equilibrium. Calculation of forensic and statistical parameters showed lower values of genetic diversity in comparison with African and European populations, as well as other, admixed populations of neighboring regions of Caribbean, Central and South America. Significant levels of divergence were observed between the four Native Venezuelan populations as well as with other previously studied populations. Analysis of the 52-plex SNP loci with Structure provided an optimum number of population clusters of three, corresponding to Africans, Europeans and Native Americans. Analysis of admixed populations indicated a range of membership proportions for ancestral populations consisting of Native American, African and European components. The genetic differences observed in the Native American groups suggested by the 52 SNPs typed in our study are in agreement with current knowledge of the demographic history of the Americas.

Typing short amplicon binary polymorphisms: supplementary SNP and Indel genetic information in the analysis of highly degraded skeletal remains.

Two sets of short amplicon binary markers (SABs): 50 single nucleotide polymorphisms (SNPs) and 38 insertion/deletion polymorphisms (Indels) were used to genotype bones of 35 years "post-mortem". Typing results of these binary markers were compared with those obtained for standard commercial STR and mini-STR DNA typing kits. We observed SAB marker performance to be better compared with conventional STR and mini-STR genotyping in degraded bone sample analysis. Furthermore, additional genetic information provided by these 88 binary markers, 50 SNPs and 38 Indels, combined with classical markers gave very high discrimination power even in severely degraded specimens, with all tested bone samples showing Random Match Probabilities (RMPs) higher than 1019. Missing person and disaster victim identification by kinship analysis is considerably strengthened by the addition of SAB markers since they can be successfully typed on degraded bone samples while adding considerable extra genetic data when poor or incomplete information is available from conventional forensic markers for the analysis of family pedigrees.

Genetic variability of the SNPforID 52-plex identification-SNP panel in Central West Colombia.

A set of autosomal single nucleotide polymorphism (SNP) loci was analyzed using the 52-plex assay previously described by Sanchez et al. [J.J. Sanchez, C. Phillips, C. Borsting, K. Balogh, M. Bogus, M. Fondevila, C.D. Harrison, E. Musgrave-Brown, A. Salas, D. Syndercombe-Court, P.M. Schneider, A. Carracedo, N. Morling, A multiplex assay with 52 single nucleotide polymorphisms for human identification, Electrophoresis 27 (2006) 1713-1724] in 140 samples of unrelated individuals born in the Colombian regions of, Risaralda, Caldas, Quindio, Antioquia, Tolima and Valle, and 164 samples of unrelated individuals with declared Native American ancestry from Colombia. Allele frequencies and statistical parameters of forensic interest are presented for the 52 SNPs. All loci were in agreement with Hardy-Weinberg equilibrium while comparisons with population samples of Argentina, Portugal, Spain, Mozambique, and Taiwan revealed significant differences in allele frequency distributions.

D9S1120, a simple STR with a common Native American-specific allele: forensic optimization, locus characterization and allele frequency studies.

The simple tetrameric STR D9S1120 exhibits a common population-specific allele of 9 repeats (9RA) reported to have an average frequency of 0.36 in Native Americans from both North and South of the continent. Apart from the presence of 9RA in two northeast Siberian populations, D9S1120 shows variability exclusive to, and universal in all American populations studied to date. This STR therefore provides an informative forensic marker applicable in countries with significant proportions of Native American populations or ancestry. We have re-designed PCR primers that reduce the amplified product sizes reported in NCBI UniSTS by more than a third and have characterized the repeat structure of D9S1120. The 9RA allele shares the same repeat structure as the majority of other D9S1120 alleles and so originates from a slippage-diminution mutation rather than an independent deletion. We confirm the previously reported allele frequencies from a range of populations indicating a global heterozygosity range for D9S1120 of 66-75% and estimate the proportion of Native American-diagnostic genotypes to average 53%, underlining the potential usefulness of this STR in both forensic identification and in population genetics studies of the Americas.

The mtDNA ancestry of admixed Colombian populations.

A total of 185 individuals from Colombia were sequenced for the first hypervariable region (HVS-I) of the mitochondrial DNA (mtDNA) genome, and a subset of these individuals were additionally genotyped for the second hypervariable segment (HVS-II). These individuals were collected according to their "self-reported ethnicity" in Colombia, comprising "Mestizos," "Mulatos," and "Afro-Colombians." We used databases containing more than 4,300 Native American lineages, 6,800 Africans, and 15,600 Europeans for population comparisons and phylogeographic inferences. We observe that Mulatos and Afro-Colombians have a dominant African mtDNA component, whereas Mestizos carry predominantly Native American haplotypes. All the populations analyzed have high diversity indices and there are no signatures of dramatic genetic drift episodes. Central and South America are the main candidate source populations of the Colombian Native American lineages, whereas west-central, southwest, and southeast Africa are the main original mtDNA sources for the African Colombian mtDNAs. We found that our results differ from those obtained in other studies for the same "population groups" in terms of haplogroup frequencies. This observation leads us to conclude that (i) self-reported ancestry is not a reliable proxy to indicate an individual's "ethnicity" in Colombia, (ii) our results do not support the use of outmoded race descriptions (Mestizos, Mulatos, etc.) mainly because these labels do not correspond to any genetically homogeneous population group, and (iii) studies relying on these terms to describe the population group of the individual, which then treat them as genetically homogeneous, carry a high risk of type I error (false positives) in medical studies in this country and of misinterpretation of the frequency of observed variation in forensic casework.

The genetic male legacy from El Salvador.

Allele frequencies and haplotype and haplogroup analysis have been performed for 16 Y-chromosome binary markers and 8 Y-chromosome STRs (DYS19, DYS385I and II, DYS389I and II, DYS390, DYS391, DYS392, DYS393). Data was obtained from a general sample of 93 unrelated individuals living in metropolitan areas from El Salvador, and 67 individuals from different historical ethnic groups, Conchagua, San Alejo, Panchimalco, Izalco and finally Nueva Concepción with white people. Levels of admixture among metropolitan and rural areas were evaluated and population substructure measured. A total of 13 haplogroups and 136 different haplotypes were found. The most frequent haplogroup in the general metropolitan population was the European R1b, while in the Indigenous samples considered as a whole the most frequent was the Amerindian haplogroup Q3.

Y-chromosome haplotype analysis in Antioquia (Colombia).

Allele frequencies and haplotype analysis have been performed for eight Y-chromosome STRs (DYS19, DYS385 I and II, DYS389 I and II, DYS390, DYS391, DYS392, DYS393). Population data was obtained from a sample of 400 unrelated individuals living in Antioquia (Colombia). A total of 270 different haplotypes were found, and the haplotype diversity was 0.989. The first and second most frequent haplotypes where shared by 8 and 6% of the individuals, respectively.

Autosomal STR genetic variation in negroid Chocó and Bogotá populations.

Genetic data for eight autosomal STRs were obtained from two different population samples from Colombia: the European Mestizo population of Bogotá and the African descent population of the Chocó region. The STRs were analysed in a multiplex system that includes the STR markers CSF1PO, TPOX, TH01, VWA, D13S317, D7S820, D16S539 and D5S818. Separation of the fragments and fluorescent detection was carried out in an ABI 310 DNA sequencer and the typing was made by comparison with sequenced allelic ladders. Exact tests were used for testing linkage between the loci and for Hardy-Weinberg equilibrium. Significant differences were found between both populations for all the loci.