A study of the peopling of Greenland using next generation sequencing of complete mitochondrial genomes

Haplogroup Structure and Genetic Variation Analyses of Mitochondrial Genome SNPs in the Iranian Population

BACKGROUND

Mitochondrial DNA (mtDNA) is a valuable marker for population studies and forensic investigations. Recent advancements in massively parallel sequencing technologies enable whole mitochondrial genome sequencing. This study collected blood samples from unrelated Iranian participants from four ethnic groups: Persian, Kurd, Lur, and Azeri. We mapped mtDNA haplogroups according to genetic ancestry and investigated the ethnic similarities within the Iranian population.

METHODS

Complete mtDNA sequences were generated with targeted mtDNA sequencing method and haplogroups were determined on the base of mitogenome polymorphisms. Additionally, we used data from the whole exome sequencing (WES) of the current samples to compare the variants identified by two different mitochondrial testing methods. Principal component analysis (PCA) calculations were performed using the R software to determine diversity between unrelated individuals of various ethnicities.

RESULTS

A total of 129 sub-haplogroups were identified in 15 main haplogroups. The findings revealed high frequencies of haplogroups U and H (22.4% and 20.3%, respectively) in the Iranian population. The PCA scatter plots revealed overlapping diversity, with no distinct trends separating the groups in these four groups within the Iranian population. In the present samples, the WES method identified only 57.8% of the variants detected by the targeted mtDNA sequencing method.

CONCLUSION

Variant studies do not show much difference, which indicate a small genetic difference between the central ethnic groups of Iran. Furthermore, comparing the targeted whole mitochondrial genome to mitochondrial data from WES in our study samples highlights the notion that targeted entire mitochondrial genome is a gold standard method for variant detection.

Performance of a 74-Microhaplotype Assay in Kinship Analyses

Microhaplotypes (MHs) consisting of multiple SNPs and indels on short stretches of DNA are new and interesting loci for forensic genetic investigations. In this study, we analysed 74 previously defined MHs in two of the populations that our laboratory provides with forensic genetic services, Danes and Greenlanders. In addition to the 229 SNPs that originally made up the 74 MHs, 66 SNPs and 3 indels were identified in the two populations, and 45 of these variants were included in new definitions of the MHs, whereas 24 SNPs were considered rare and of little value for case work. The average effective number of alleles (Ae) was 3.2, 3.0, and 2.6 in Danes, West Greenlanders, and East Greenlanders, respectively. High levels of linkage disequilibrium were observed in East Greenlanders, which reflects the characteristics of this population that has a small size, and signs of admixture and substructure. Pairwise kinship simulations of full siblings, half-siblings, first cousins, and unrelated individuals were performed using allele frequencies from MHs, STRs and SNPs from Danish and Greenlandic populations. The MH panel outperformed the currently used STR and SNP marker sets and was able to differentiate siblings from unrelated individuals with a 0% false positive rate and a 1.1% false negative rate using an LR threshold of 10,000 in the Danish population. However, the panel was not able to differentiate half-siblings or first cousins from unrelated individuals. The results generated in this study will be used to implement MHs as investigative markers for relationship testing in our laboratory.

The Mitochondrial DNA Landscape of Modern Mexico

Mexico is a rich source for anthropological and population genetic studies with high diversity in ethnic and linguistic groups. The country witnessed the rise and fall of major civilizations, including the Maya and Aztec, but resulting from European colonization, the population landscape has dramatically changed. Today, the majority of Mexicans do not identify themselves as Indigenous but as admixed, and appear to have very little in common with their pre-Columbian predecessors. However, when the maternally inherited mitochondrial (mt)DNA is investigated in the modern Mexican population, this is not the case. Control region sequences of 2021 samples deriving from all over the country revealed an overwhelming Indigenous American legacy, with almost 90% of mtDNAs belonging to the four major pan-American haplogroups A2, B2, C1, and D1. This finding supports a very low European contribution to the Mexican gene pool by female colonizers and confirms the effectiveness of employing uniparental markers as a tool to reconstruct a country’s history. In addition, the distinct frequency and dispersal patterns of Indigenous American and West Eurasian clades highlight the benefit such large and country-wide databases provide for studying the impact of colonialism from a female perspective and population stratification. The importance of geographical database subsets not only for forensic application is clearly demonstrated.

Haplogroup Structure and Genetic Variation Analyses of 60 Mitochondrial DNA Markers in Southern Shaanxi Han Population

Mitochondrial DNA (mtDNA) has been widely employed as one tool for the studies of human migration and phylogenetic evolution owing to the characteristics of its lack of recombination and matrilineal inheritance. In this study, we analyze genetic distributions of 60 mtDNA markers in 126 unrelated individuals of Southern Shaanxi Han population and classify their haplogroups. Genetic distribution comparisons between Southern Shaanxi Han and other populations from different continents are conducted based on the same mtDNA markers. The majority of 60 mtDNA markers are polymorphic in Southern Shaanxi Han population. The most common haplogroups observed in Southern Shaanxi Han population are B5, followed by D5, A, D4e, and N9a1'3. Obtained matching probability for these 60 mtDNA markers indicates that the panel could be used as a valuable tool in forensic caseworks. Results of genetic distances (Fst) and multidimensional scaling analysis show that Southern Shaanxi Han population has relatively close genetic relationships with other Han populations in different regions. In conclusion, the panel comprising 60 mtDNA markers could be utilized for forensic applications in Southern Shaanxi Han population.

MtDNA polymorphism analyses in the Chinese Mongolian group: Efficiency evaluation and further matrilineal genetic structure exploration

BACKGROUND

Profiling of mitochondrial DNA is surely to provide valuable investigative clues for forensic cases involving highly degraded specimens or complex maternal lineage kinship determination. But traditionally used hypervariable region sequencing of mitochondrial DNA is less frequently suggested by the forensic community for insufficient informativeness. Genome-wide sequencing of mitochondrial DNA can provide considerable amount of variant information but can be high cost at the same time.

METHODS

Efficiency of the 60 mitochondrial DNA polymorphic sites dispersing across the control region and coding region of mitochondrial DNA genome was evaluated with 106 Mongolians recruited from the Xinjiang Uyghur Autonomous Region, China, and allele-specific PCR technique was employed for mitochondrial DNA typing.

RESULTS

Altogether 58 haplotypes were observed and the haplotypic diversity, discrimination power and random match probability were calculated to be 0.981, 0.972, and 0.028, respectively. Mitochondrial DNA haplogroup affiliation exhibited an exceeding percentage (12.26%) of west Eurasian lineage (H haplogroup) in the studied Mongolian group, which needed to be further verified with more samples. Furthermore, the genetic relationships between the Xinjiang Mongolian group and the comparison populations were also investigated and the genetic affinity was discovered between the Xinjiang Mongolian group and the Xinjiang Kazak group in this study.

CONCLUSION

It was indicated that the panel was potentially enough to be used as a supplementary tool for forensic applications. And the matrilineal genetic structure analyses based on mitochondrial DNA variants in the Xinjiang Mongolian group could be helpful for subsequent anthropological studies.

Analysis of Uyghur and Kazakh populations using the Precision ID Ancestry Panel

Autosomal ancestry informative markers (AIMs) are important markers for inferring ancestry of humans. In the present study, we typed 105 Uyghurs and 94 Kazakhs with the Precision ID Ancestry Panel that amplifies 165 autosomal AIMs. No statistically significant deviation from Hardy-Weinberg equilibrium and no linkage disequilibrium between loci was observed after Bonferroni correction. STRUCTURE and PCA analyses showed that Uyghurs and Kazakhs appeared as admixed individuals of primarily European and East Asian ancestry and were clearly differentiated from Europeans, Middle Easterners, South/Central Asians, and East Asians. However, it was not possible to differentiate the two populations from each other and they were also difficult to differentiate from Greenlanders, a population with European/Inuit admixture. GenoGeographer was used to evaluate the weight of the evidence. Initially, the results showed that the majority of AIM profiles from Uyghur and Kazakh individuals were not represented by any of the 36 reference populations of the GenoGeographer database. Consequently, it was not reasonable to infer the ancestry of these individuals. A randomly selected subset of the studied populations (75 Uyghur and 75 Kazakh individuals) was used to construct two new reference populations for GenoGeographer, and ancestry prediction was performed on the remaining test individuals. A total of 42 out of 49 test individuals were represented by at least one population after the introduction of Uyghur and Kazakh reference populations. Likelihood ratios ≥10⁶ were obtained when the alternative hypothesis was that the individual belonged to the South/Central Asian, East Asian, Middle Eastern, European, or the admixed Greenlandic population.

Mitochondrial DNA in human identification: a review

Mitochondrial DNA (mtDNA) presents several characteristics useful for forensic studies, especially related to the lack of recombination, to a high copy number, and to matrilineal inheritance. mtDNA typing based on sequences of the control region or full genomic sequences analysis is used to analyze a variety of forensic samples such as old bones, teeth and hair, as well as other biological samples where the DNA content is low. Evaluation and reporting of the results requires careful consideration of biological issues as well as other issues such as nomenclature and reference population databases. In this work we review mitochondrial DNA profiling methods used for human identification and present their use in the main cases of humanidentification focusing on the most relevant issues for forensics.

A new self-learning computational method for footprints of early human migration processes

We present a new self-learning computational method searching for footprints of early migration processes determining the genetic compositions of recent human populations. The data being analysed are 26- and 18-dimensional mitochondrial and Y-chromosomal haplogroup distributions representing 50 recent and 34 ancient populations in Eurasia and America. The algorithms search for associations of haplogroups jointly propagating in a significant subset of these populations. Joint propagations of Hgs are detected directly by similar ranking lists of populations derived from Hg frequencies of the 50 Hg distributions. The method provides us the most characteristic associations of mitochondrial and Y-chromosomal haplogroups, and the set of populations where these associations propagate jointly. In addition, the typical ranking lists characterizing these Hg associations show the geographical distribution, the probable place of origin and the paths of their protection. Comparison to ancient data verifies that these recent geographical distributions refer to the most important prehistoric migrations supported by archaeological evidences.

Deep-Coverage MPS Analysis of Heteroplasmic Variants within the mtGenome Allows for Frequent Differentiation of Maternal Relatives

Distinguishing between maternal relatives through mitochondrial (mt) DNA sequence analysis has been a longstanding desire of the forensic community. Using a deep-coverage, massively parallel sequencing (DCMPS) approach, we studied the pattern of mtDNA heteroplasmy across the mtgenomes of 39 mother-child pairs of European decent; haplogroups H, J, K, R, T, U, and X. Both shared and differentiating heteroplasmy were observed on a frequent basis in these closely related maternal relatives, with the minor variant often presented as 2–10% of the sequencing reads. A total of 17 pairs exhibited differentiating heteroplasmy (44%), with the majority of sites (76%, 16 of 21) occurring in the coding region, further illustrating the value of conducting sequence analysis on the entire mtgenome. A number of the sites of differentiating heteroplasmy resulted in non-synonymous changes in protein sequence (5 of 21), and to changes in transfer or ribosomal RNA sequences (5 of 21), highlighting the potentially deleterious nature of these heteroplasmic states. Shared heteroplasmy was observed in 12 of the 39 mother-child pairs (31%), with no duplicate sites of either differentiating or shared heteroplasmy observed; a single nucleotide position (16093) was duplicated between the data sets. Finally, rates of heteroplasmy in blood and buccal cells were compared, as it is known that rates can vary across tissue types, with similar observations in the current study. Our data support the view that differentiating heteroplasmy across the mtgenome can be used to frequently distinguish maternal relatives, and could be of interest to both the medical genetics and forensic communities.

Massively parallel sequencing-enabled mixture analysis of mitochondrial DNA samples

The mitochondrial genome has a number of characteristics that provide useful information to forensic investigations. Massively parallel sequencing (MPS) technologies offer improvements to the quantitative analysis of the mitochondrial genome, specifically the interpretation of mixed mitochondrial samples. Two-person mixtures with nuclear DNA ratios of 1:1, 5:1, 10:1, and 20:1 of individuals from different and similar phylogenetic backgrounds and three-person mixtures with nuclear DNA ratios of 1:1:1 and 5:1:1 were prepared using the Precision ID mtDNA Whole Genome Panel and Ion Chef, and sequenced on the Ion PGM or Ion S5 sequencer (Thermo Fisher Scientific, Waltham, MA, USA). These data were used to evaluate whether and to what degree MPS mixtures could be deconvolved. Analysis was effective in identifying the major contributor in each instance, while SNPs from the minor contributor's haplotype only were identified in the 1:1, 5:1, and 10:1 two-person mixtures. While the major contributor was identified from the 5:1:1 mixture, analysis of the three-person mixtures was more complex, and the mixed haplotypes could not be completely parsed. These results indicate that mixed mitochondrial DNA samples may be interpreted with the use of MPS technologies.