Miriam Baeta

Continent-Wide Decoupling of Y-Chromosomal Genetic Variation from Language and Geography in Native South Americans

Numerous studies of human populations in Europe and Asia have revealed a concordance between their extant genetic structure and the prevailing regional pattern of geography and language. For native South Americans, however, such evidence has been lacking so far. Therefore, we examined the relationship between Y-chromosomal genotype on the one hand, and male geographic origin and linguistic affiliation on the other, in the largest study of South American natives to date in terms of sampled individuals and populations. A total of 1,011 individuals, representing 50 tribal populations from 81 settlements, were genotyped for up to 17 short tandem repeat (STR) markers and 16 single nucleotide polymorphisms (Y-SNPs), the latter resolving phylogenetic lineages Q and C. Virtually no structure became apparent for the extant Y-chromosomal genetic variation of South American males that could sensibly be related to their inter-tribal geographic and linguistic relationships. This continent-wide decoupling is consistent with a rapid peopling of the continent followed by long periods of isolation in small groups. Furthermore, for the first time, we identified a distinct geographical cluster of Y-SNP lineages C-M217 (C3*) in South America. Such haplotypes are virtually absent from North and Central America, but occur at high frequency in Asia. Together with the locally confined Y-STR autocorrelation observed in our study as a whole, the available data therefore suggest a late introduction of C3* into South America no more than 6,000 years ago, perhaps via coastal or trans-Pacific routes. Extensive simulations revealed that the observed lack of haplogroup C3* among extant North and Central American natives is only compatible with low levels of migration between the ancestor populations of C3* carriers and non-carriers. In summary, our data highlight the fact that a pronounced correlation between genetic and geographic/cultural structure can only be expected under very specific conditions, most of which are likely not to have been met by the ancestors of native South Americans.

Reconstructing the population history of Nicaragua by means of mtDNA, Y‐chromosome STRs, and autosomal STR markers

Before the arrival of the Spaniards in Nicaragua, diverse Native American groups inhabited the territory. In colonial times, Native Nicaraguan populations interacted with Europeans and slaves from Africa. To ascertain the extent of this genetic admixture and provide genetic evidence about the origin of the Nicaraguan ancestors, we analyzed the mitochondrial control region (HVSI and HVSII), 17 Y chromosome STRs, and 15 autosomal STRs in 165 Mestizo individuals from Nicaragua. To carry out interpopulation comparisons, HVSI sequences from 29 American populations were compiled from the literature. The results reveal a close relationship between Oto-manguean, Uto-Aztecan, Mayan groups from Mexico, and a Chibchan group to Nicaraguan lineages. The Native American contribution to present-day Nicaraguan Mestizos accounts for most of the maternal lineages, whereas the majority of Nicaraguan Y chromosome haplogroups can be traced back to a West Eurasian origin. Pairwise Fst distances based on Y-STRs between Nicaragua and European, African and Native American populations show that Nicaragua is much closer to Europeans than the other populations. Additionally, admixture proportions based on autosomal STRs indicate a predominantly Spanish contribution. Our study reveals that the Nicaraguan Mestizo population harbors a high proportion of European male and Native American female substrate. Finally, the amount of African ancestry is also interesting, probably because of the contribution of Spanish conquerors with North African genetic traces or that of West African slaves.

Association between ancient bone preservation and dna yield: A multidisciplinary approach

Ancient molecular typing depends on DNA survival in archaeological bones. Finding valuable tools to predict DNA presence in ancient samples, which can be measured prior to undertaking a genetic study, has become an important issue as a consequence of the peculiarities of archaeological samples. Since the survival of DNA is explained by complex interrelations of multiple variables, the aim of the present study was to analyze morphological, structural, chemical, and biological aspects of a set of medieval human bones, to provide an accurate reflection of the state of preservation of the bony components and to relate it with DNA presence. Archaeological bones that yielded amplifiable DNA presented high collagen content (generally more than 12%), low racemization values of aspartic acid (lesser than 0.08), leucine and glutamic acid, low infrared splitting factor, small size of crystallite, and more compact appearance of bone in the scanning electron micrographs. Whether these patterns are characteristic of ancient bones or specific of each burial site or specimen requires further investigation.

Y chromosome haplogroup diversity in a Mestizo population of Nicaragua

Y chromosome single nucleotide polymorphisms (Y-SNPs) are indispensable markers for haplogroup determination. Since Y chromosome haplogroups show a high specific geographical distribution, they play a major role in population genetics but can also benefit forensic investigations. Although haplogroup prediction methods based on Y chromosome short tandem repeats (Y-STRs) exist and are frequently used, precaution is required in this regard. In this study we determine the Y chromosome haplogroups of a Nicaraguan population using several Y-SNP multiplex reactions. Y chromosome haplogroups have been predicted before, but our results show that a confirmation with Y-SNP typings is necessary. These results have revealed a 4.8% of error in haplogroup prediction based on Y-STR haplotypes using Atheys Haplogroup Predictor. The Nicaraguan Mestizo population displays a majority of Eurasian lineages, mainly represented by haplogroup R-M207 (46.7%). Other Eurasian lineages have been observed, especially J-P209 (13.3%), followed by I-M170 (3.6%) and G-M201 (1.8%). Haplogroup E-P170 was also observed in 15.2% of the sample, particularly subhaplogroup E1b1b1-M35. Finally, the Native American haplogroup Q-M242 was found in 15.2% of the sample, with Q1a3a-M3 being the most frequent.

Mitochondrial diversity in Amerindian Kichwa and Mestizo populations from Ecuador

This study presents mitochondrial DNA (mtDNA) data from 107 unrelated individuals from two of the major ethnic groups in Ecuador: Amerindian Kichwas (n = 65) and Mestizos (n = 42). We characterized the diversity of the matrilineal lineages of these Ecuadorian groups by analyzing the entire mtDNA control region. Different patterns of diversity were observed in the two groups as result of the unique historical and demographic events which have occurred in each population. Higher genetic diversity values were obtained for the Mestizo group than for the Amerindian group. Interestingly, only Native American lineages were detected in the two population samples, but with differences in the haplogroup distribution: Kichwa (A, 49%; B, 3%; C, 8%; and D, 40%) and Mestizo (A, 33%; B, 33%; C, 10%; and D, 24%). Analysis of the complete mtDNA control region proved to be useful to increase the discrimination power between individuals who showed common haplotypes in HVSI and HVSII segments; and added valuable information to the phylogenetic interpretation of mtDNA haplotypes.

Nuclear DNA typing from ancient teeth.

AbstractBecause of the adverse effects that diagenesis exert on ancient skeletal remains, DNA from these samples is often compromised to the point where genetic typing can be challenging. Nevertheless, robust and reliable methods are currently available to allow successful genotyping of ancient specimens. Here we report nuclear DNA–based methods and typing strategies used to analyze 2 human skeletons from a medieval burial. Reliable DNA nuclear profiles were obtained from teeth, whereas mitochondrial DNA analyses in bones were inconclusive. A complete nuclear mini short tandem repeat profile was obtained from a well-preserved premolar, but only a partial one from the femur. Increasing the sensitivity of the polymerase chain reaction system allowed a full profile from the latter, but the presence of artifacts reinforced the idea that the interpretation of this kind of analysis must be performed with caution. The results presented here also indicate that DNA from dental pieces can be better preserved than from bones, even in the case of well-preserved long bones with thick cortical tissue such as the femurs, and have a better chance of successful genetic typing, probably because of the high degree of protection conferred to the DNA by the enamel.

Genetic analysis of 7 medieval skeletons from the Aragonese Pyrenees.

Aim To perform a genetic characterization of 7 skeletons from medieval age found in a burial site in the Aragonese Pyrenees. Methods Allele frequencies of autosomal short tandem repeats (STR) loci were determined by 3 different STR systems. Mitochondrial DNA (mtDNA) and Y-chromosome haplogroups were determined by sequencing of the hypervariable segment 1 of mtDNA and typing of phylogenetic Y chromosome single nucleotide polymorphisms (Y-SNP) markers, respectively. Possible familial relationships were also investigated. Results Complete or partial STR profiles were obtained in 3 of the 7 samples. Mitochondrial DNA haplogroup was determined in 6 samples, with 5 of them corresponding to the haplogroup H and 1 to the haplogroup U5a. Y-chromosome haplogroup was determined in 2 samples, corresponding to the haplogroup R. In one of them, the sub-branch R1b1b2 was determined. mtDNA sequences indicated that some of the individuals could be maternally related, while STR profiles indicated no direct family relationships. Conclusions Despite the antiquity of the samples and great difficulty that genetic analyses entail, the combined use of autosomal STR markers, Y-chromosome informative SNPs, and mtDNA sequences allowed us to genotype a group of skeletons from the medieval age.

Analysis of 10 X-STRs in three population groups from Ecuador.

X-chromosomal short tandem repeat (X-STR) loci provide a useful tool for forensic purposes [1]. Due to a sex-based mode of inheritance, the use of this genetic system has become extremely valuable in paternity testing, especially in deficiency cases involving female offspring [2]. Ecuador is a multi-ethnic country in which the admixed population of Mestizos represents 72% of the population while Native Americans account for 7% with Kichwa being the largest [3]. A second population deserving interest is the Waorani, the last population of Native American hunter-gatherers in the Eastern region of the nation. The population is composed of 3000 individuals [4] and has been previously characterized as genetically unique [5] attributed to prolonged isolation, high inbreeding and low population size. Previous studies focused on autosomal and uniparentally inherited markers [6–11] have shown evidence of the high diversity existing in the Ecuadorian population as a result of its complex history and multi-ethnic richness. However, current information on the variability of X-chromosome in Ecuador is limited [5]. This study aimed to explore the genetic structure and dynamics of Ecuadorian Waorani, Kichwa and Mestizo populations from the perspective of the X chromosome based on 10 X-STRs [12]. A population sample of 139 maternally unrelated individuals born and living in Ecuador were selected: 32 Waoranis (17 males and 15 females) and 65 Kichwas (27 males and 38 females) from the Amazonian provinces; and 42 Mestizos (28 males and 14 females) from different regions of the country. All donors gave their informed consent prior to their inclusion in the study. DNA was extracted from saliva swab samples and blood stains on FTA cards (Whatman Inc., Clifton, NJ) using the Chelex extraction procedure [13]. X-STR amplification (DXS8378, DXS9898, DXS7133, GATA31E08, GATA172D05, DXS7423, DXS6809, DXS7132, DXS9902 and DXS6789) was performed according to Gusmao et al. [12]. Alleles were separated and detected using an ABI Prism 3130 Genetic Analyzer (Applied Biosystems, Foster City, CA). Allele frequencies were calculated using the direct counting method. Gene diversities, Hardy– Weinberg equilibrium (females), linkage disequilibrium (males) and pairwise exact test of population differentiation were tested using Arlequin software v3.0 [14]. Pairwise population comparisons between the Ecuadorian populations were performed at a single locus level (exact test of population differentiation and Fst genetic distance analysis) and for the 10 X-STRs (Fst genetic distance analysis). Additionally, pairwise Fst genetic distances were calculated between the populations from Ecuador and other available populations with the same 10 X-STRs [15–20]. Unweighted pair group method with arithmetic mean was used to build a phylogenetic tree based on Fst distances using the option

Differentially methylated CpG regions analyzed by PCR-high resolution melting for monozygotic twin pair discrimination

Discrimination between monozygotic (MZ) twins is a forensic limitation when using conventional DNA profiling techniques for human identification. Recent works based on epigenetics seem to open a new way to solve this issue due to methylation status of MZ twins change during their lifetime. Methylation analysis through BeadChip platforms allows the study up to 850 K CpG sites revealing that numerous differential methylation regions exist between MZ twins. However, this methodology is difficult to implement in forensic laboratories. On the contrary, PCR-HRM (High Resolution Melting) technology is one of the easiest methods for analyzing DNA methylation and it has been capable to discriminate between MZ twins. The purpose of this study is to contribute with new differential methylation regions in MZ twins to those that have been previously studied through PCR-HRM. Here, we have selected 6 CpG regions located at the ITGA2B, ASPA, PDE4C, ZIC5, USP11 and NOP14 loci that have shown methylation status variation during lifetime. The study has been carried out from saliva-derived DNA of 18 MZ twin pairs. The most discriminating regions were those located at ITGA2B, ASPA and ZIC5 loci showing significant within-pair differences in 44.4% of the cases. Non evidences of relation between age and significant differences between MZ twins were found, although the 50% of MZ twin pairs were discrimnated in the oldest age range (59-66 years old). These results support the use of these regions to increase the number of epigenetics age-related markers available to discriminate between MZ twins in a pair by PCR-HRM in forensic laboratories.

Different Evolutionary History for Basque Diaspora Populations in USA and Argentina Unveiled by Mitochondrial DNA Analysis.

The Basque Diaspora in Western USA and Argentina represents two populations which have maintained strong Basque cultural and social roots in a completely different geographic context. Hence, they provide an exceptional opportunity to study the maternal genetic legacy from the ancestral Basque population and assess the degree of genetic introgression from the host populations in two of the largest Basque communities outside the Basque Country. For this purpose, we analyzed the complete mitochondrial DNA control region of Basque descendants living in Western USA (n = 175) and in Argentina (n = 194). The Diaspora populations studied here displayed a genetic diversity in their European maternal input which was similar to that of the Basque source populations, indicating that not important founder effects would have occurred. Actually, the genetic legacy of the Basque population still prevailed in their present-day maternal pools, by means of a haplogroup distribution similar to the source population characterized by the presence of autochthonous Basque lineages, such as U5b1f1a and J1c5c1. However, introgression of non-Basque lineages, mostly Native American, has been observed in the Diaspora populations, particularly in Argentina, where the quick assimilation of the newcomers would have favored a wider admixture with host populations. In contrast, a longer isolation of the Diaspora groups in USA, because of language and cultural differences, would have limited the introgression of local lineages. This study reveals important differences in the maternal evolutionary histories of these Basque Diaspora populations, which have to be taken into consideration in forensic and medical genetic studies.