Community-engaged ancient DNA project reveals diverse origins of 18th-century African descendants in Charleston, South Carolina.

In this study, we present the results of community-engaged ancient DNA research initiated after the remains of 36 African-descended individuals dating to the late 18th century were unearthed in the port city of Charleston, South Carolina. The Gullah Society of Charleston, along with other Charleston community members, initiated a collaborative genomic study of these ancestors of presumed enslaved status, in an effort to visibilize their histories. We generated 18 low-coverage genomes and 31 uniparental haplotypes to assess their genetic origins and interrelatedness. Our results indicate that they have predominantly West and West-Central African genomic ancestry, with one individual exhibiting some genomic affiliation with populations in the Americas. Most were assessed as genetic males, and no autosomal kin were identified among them. Overall, this study expands our understanding of the colonial histories of African descendant populations in the US South.

Evolution and dispersal of mitochondrial DNA haplogroup U5 in Northern Europe: insights from an unsupervised learning approach to phylogeography.

BACKGROUND: We combined an unsupervised learning methodology for analyzing mitogenome sequences with maximum likelihood (ML) phylogenetics to make detailed inferences about the evolution and diversification of mitochondrial DNA (mtDNA) haplogroup U5, which appears at high frequencies in northern Europe. METHODS: Haplogroup U5 mitogenome sequences were gathered from GenBank. The hierarchal Bayesian Analysis of Population Structure (hierBAPS) method was used to generate groups of sequences that were then projected onto a rooted maximum likelihood (ML) phylogenetic tree to visualize the pattern of clustering. The haplogroup statuses of the individual sequences were assessed using Haplogrep2. RESULTS: A total of 23 hierBAPS groups were identified, all of which corresponded to subclades defined in Phylotree, v.17. The hierBAPS groups projected onto the ML phylogeny accurately clustered all haplotypes belonging to a specific haplogroup in accordance with Haplogrep2. By incorporating the geographic source of each sequence and subclade age estimates into this framework, inferences about the diversification of U5 mtDNAs were made. Haplogroup U5 has been present in northern Europe since the Mesolithic, and spread in both eastern and western directions, undergoing significant diversification within Scandinavia. A review of historical and archeological evidence attests to some of the population interactions contributing to this pattern. CONCLUSIONS: The hierBAPS algorithm accurately grouped mitogenome sequences into subclades in a phylogenetically robust manner. This analysis provided new insights into the phylogeographic structure of haplogroup U5 diversity in northern Europe, revealing a detailed perspective on the diversity of subclades in this region and their distribution in Scandinavian populations.

Genetic variation in the E6 and E7 genes of human papillomavirus type 16 in northeastern Argentina.

The province of Misiones is considered a region with a high mortality rate due to cervical cancer (CC). To gain insight into this problem, we explored the association between genetic variation in the E6 and E7 oncogenes of HPV16 and the risk of CC. We studied 160 women with cytological diagnoses of negative for intraepithelial lesion or malignity, low-grade squamous intraepithelial lesion, and high-grade squamous intraepithelial lesion/CC and a positive test for HPV16 infection. The genetic characterization of E6 and E7 genes was undertaken through PCR amplification and direct Sanger sequencing. Phylogenetic classification was conducted using Bayesian methods. To estimate the odds ratio (OR) for an association between genetic variants in the E6 and E7 genes and the risk of CC, we used ordinal logistic regression adjusted by age. The final data set comprised 112 samples. Diagnostic single-nucleotide polymorphisms (SNPs) and phylogenetic trees confirmed the presence of Lineage A (95.5%) and D (4.5%) in the samples. For the E6 gene, we identified eleven different sequences, with the most common ones being Lineage A E6 350G (58.9%) and E6 350T (37.5%). The E6 350G was associated with progression to HSIL/CC, with an OR of 19.41 (4.95-76.10). The E7 gene was more conserved than E6, probably due to the functional constraints of this small protein. Our results confirmed the association of the E6 350G SNP with a higher risk of developing CC. These data will contribute to understanding the biological bases of CC incidence in this region.

Mitochondrial genetic variation in human bioenergetics, adaptation, and adult disease.

OBJECTIVES: Mitochondria are critical for the survival of eukaryotic organisms due to their ability to produce cellular energy, which drives virtually all aspects of host biology. However, the effects of mitochondrial DNA (mtDNA) variation in relation to disease etiology and adaptation within contemporary global human populations remains incompletely understood. METHODS: To develop a more holistic understanding of the role of mtDNA diversity in human adaptation, health, and disease, we investigated mitochondrial biology and bioenergetics. More specifically, we synthesized details from studies of mitochondrial function and variation in the context of haplogroup background, climatic adaptation, and oxidative disease. RESULTS: The majority of studies show that mtDNA variation arose during modern human dispersal around the world. Some of these variants appear to have been positively selected for their adaptiveness in colder climates, with these sequence changes having implications for tissue-specific function and thermogenic capacity. In addition, many variants modulating energy production are also associated with damaging metabolic byproducts and mitochondrial dysfunction, which, in turn, are implicated in the onset and severity of several different adult mitochondrial diseases. Thus, mtDNA variation that governs bioenergetics, metabolism, and thermoregulation may potentially have adverse consequences for human health, depending on the genetic background and context in which it occurs. CONCLUSIONS: Our review suggests that the mitochondrial research field would benefit from independently replicating mtDNA haplogroup-phenotype associations across global populations, incorporating potentially confounding environmental, demographic, and disease covariates into studies of mtDNA variation, and extending association-based studies to include analyses of complete mitogenomes and assays of mitochondrial function.

Matrilineal diversity and population history of Norwegians.

BACKGROUND: While well known for its Viking past, Norway's population history and the influences that have shaped its genetic diversity are less well understood. This is particularly true with respect to its demography, migration patterns, and dialectal regions, despite there being curated historical records for the past several centuries. In this study, we undertook an analysis of mitochondrial DNA (mtDNA) diversity within the country to elaborate this history from a matrilineal genetic perspective. METHODS: We aggregated 1174 partial modern Norwegian mtDNA sequences from the published literature and subjected them to detailed statistical and phylogenetic analysis by dialectal regions and localities. We further contextualized the matrilineal ancestry of modern Norwegians with data from Mesolithic, Iron Age, and historic period populations. RESULTS: Modern Norwegian mtDNAs fell into eight West Eurasian (N, HV, JT, I, U, K, X, W), five East Eurasian (A, F, G, N11, Z), and one African (L2) haplogroups. Pairwise analysis of molecular variance (AMOVA) estimates for all Norwegians indicated they were differentiated from each other at 1.68% (p < 0.001). Norwegians within the same dialectal region also showed genetic similarities to each other, although differences between subpopulations within dialectal regions were also observed. In addition, certain mtDNA lineages in modern Norwegians were also found among prehistoric and historic period populations, suggesting some level of genetic continuity over hundreds to many thousands of years. CONCLUSIONS: This analysis of mtDNA diversity provides a detailed picture of the genetic variation within Norway in light of its topography, settlement history, and historical migrations over the past several centuries.

Ancestry, health, and lived experiences of enslaved Africans in 18th century Charleston: An osteobiographical analysis.

OBJECTIVES: In 2013, the burials of 36 individuals of putative African ancestry were discovered during renovation of the Gaillard Center in downtown Charleston, South Carolina. The Charleston community facilitated a bioarchaeological and mitogenomic study to gain insights into the lives of these unknown persons, referred to as the Anson Street Ancestors, including their ancestry, health, and lived experiences in the 18th century. METHODS: Metric and morphological assessments of skeletal and dental characteristics were recorded, and enamel and cortical bone strontium stable isotope values generated. Whole mitochondrial genomes were sequenced and analyzed. RESULTS: Osteological analysis identified adults, both females and males, and subadults at the site, and estimated African ancestry for most individuals. Skeletal trauma and pathology were infrequent, but many individuals exhibited dental decay and abscesses. Strontium isotope data suggested these individuals mostly originated in Charleston or sub-Saharan Africa, with many being long-term residents of Charleston. Nearly all had mitochondrial lineages belonging to African haplogroups (L0-L3, H1cb1a), with two individuals sharing the same L3e2a haplotype, while one had a Native American A2 mtDNA. DISCUSSION: This study generated detailed osteobiographies of the Anson Street Ancestors, who were likely of enslaved status. Our results indicate that the Ancestors have diverse maternal African ancestries and are largely unrelated, with most being born locally. These details reveal the demographic impact of the trans-Atlantic slave trade. Our analysis further illuminates the lived experiences of individuals buried at Anson Street, and expands our understanding of 18th century African history in Charleston.

Genetic landscape of Gullah African Americans.

OBJECTIVES: Gullah African Americans are descendants of formerly enslaved Africans living in the Sea Islands along the coast of the southeastern U.S., from North Carolina to Florida. Their relatively high numbers and geographic isolation were conducive to the development and preservation of a unique culture that retains deep African features. Although historical evidence supports a West-Central African ancestry for the Gullah, linguistic and cultural evidence of a connection to Sierra Leone has led to the suggestion of this country/region as their ancestral home. This study sought to elucidate the genetic structure and ancestry of the Gullah. MATERIALS AND METHODS: We leveraged whole-genome genotype data from Gullah, African Americans from Jackson, Mississippi, African populations from Sierra Leone, and population reference panels from Africa and Europe to infer population structure, ancestry proportions, and global estimates of admixture. RESULTS: Relative to non-Gullah African Americans from the Southeast US, the Gullah exhibited higher mean African ancestry, lower European admixture, a similarly small Native American contribution, and increased male-biased European admixture. A slightly tighter bottleneck in the Gullah 13 generations ago suggests a largely shared demographic history with non-Gullah African Americans. Despite a slightly higher relatedness to populations from Sierra Leone, our data demonstrate that the Gullah are genetically related to many West African populations. DISCUSSION: This study confirms that subtle differences in African American population structure exist at finer regional levels. Such observations can help to inform medical genetics research in African Americans, and guide the interpretation of genetic data used by African Americans seeking to explore ancestral identities.

Mitochondrial DNA diversity in the Khattak and Kheshgi of the Peshawar Valley, Pakistan.

The strategic location of Pakistan and its presence at the crossroads of Asia has resulted in it playing a central role in both prehistoric and historic human migratory events, thereby linking and facilitating contacts between the inhabitants of the Middle East, Central Asia, China and South Asia. Despite the importance of this region and its inhabitants for our understanding of modern human origins and population dispersals, the nature of mitochondrial DNA (mtDNA) variation among members of the myriad populations of this area has largely been unexplored. Here, we report mtDNA control region sequences in 58 individuals from the Khattak and the Kheshgi, two major Pakhtun tribes residing within the Peshawar Valley of northwestern Pakistan. The results reveal that these ethnic groups are genetically heterogeneous, having 55.7% West Eurasian, 33.9% South Asian and 10.2% East Asian haplogroups. The genetic diversity observed for the Kheshgi was somewhat higher than that of the Khattak. A multidimensional scaling plot based on haplogroup frequencies for the Khattak, Kheshgi and neighboring populations indicates that the Khattak have close affinities with Baluch, Uzbek and Kazak populations but are only distantly related to the Kheshgi and other Pakistani populations. By contrast, the Kheshgi cluster closely with other Pakhtun or Pathan populations of Pakistan, suggesting a possible common maternal gene pool shared amongst them. These mtDNA data allow us to begin reconstructing the origins of the Khattak and Kheshgi and describe their complex interactions with populations from the surrounding regions.

Ancient DNA and bioarchaeological perspectives on European and African diversity and relationships on the colonial Delaware frontier.

OBJECTIVES: Ancient DNA (aDNA) and standard osteological analyses applied to 11 skeletons at a late 17th to early 18th century farmstead site in Delaware to investigate the biological and social factors of settlement and slavery in colonial America. MATERIALS AND METHODS: Osteological analysis and mitochondrial DNA (mtDNA) sequencing were conducted for all individuals and the resulting data contextualized with archaeological and documentary evidence. RESULTS: Individuals of European and African descent were spatially separated in this colonial cemetery. The skeletal remains exhibited differences in osteological features and maternal genetic ancestry. A specific mtDNA haplotype appeared in a subset of the European-descended individuals suggesting they were maternally related. Individuals of African descent were not maternally related, and instead showed a diversity of haplotypes affiliated with present-day Western, Central, and Eastern regions of Africa. DISCUSSION: Along with the bioarchaeological and documentary evidence, the aDNA findings contribute to our understanding of life on the colonial Delaware frontier. Evidence of maternal relatedness among European-descended individuals at the site demonstrates kin-based settlements in 17th century Delaware and provides preliminary identifications of individuals. The maternal genetic diversity of the individuals with African descent aligns with the routes of the trans-Atlantic slave trade but broadens our understanding of the ancestries of persons involved in it. Burial positioning, osteological pathology, and lack of maternal kinship among individuals of African descent provide tangible evidence for the emergence of racialized labor and society in Delaware during the late 17th century.

Analysis of biogeographic ancestry reveals complex genetic histories for indigenous communities of St. Vincent and Trinidad.

OBJECTIVES: From a genetic perspective, relatively little is known about how mass emigrations of African, European, and Asian peoples beginning in the 16th century affected Indigenous Caribbean populations. Therefore, we explored the impact of serial colonization on the genetic variation of the first Caribbean islanders. MATERIALS AND METHODS: Sixty-four members of St. Vincent's Garifuna Community and 36 members of Trinidad's Santa Rosa First People's Community (FPC) of Arima were characterized for mitochondrial DNA and Y-chromosome diversity via direct sequencing and targeted SNP and STR genotyping. A subset of 32 Garifuna and 18 FPC participants were genotyped using the GenoChip 2.0 microarray. The resulting data were used to examine genetic diversity, admixture, and sex biased gene flow in the study communities. RESULTS: The Garifuna were most genetically comparable to African descendant populations, whereas the FPC were more similar to admixed American groups. Both communities also exhibited moderate frequencies of Indigenous American matrilines and patrilines. Autosomal SNP analysis indicated modest Indigenous American ancestry in these populations, while both showed varying degrees of African, European, South Asian, and East Asian ancestry, with patterns of sex-biased gene flow differing between the island communities. DISCUSSION: These patterns of genetic variation are consistent with historical records of migration, forced, or voluntary, and suggest that different migration events shaped the genetic make-up of each island community. This genomic study is the highest resolution analysis yet conducted with these communities, and provides a fuller understanding of the complex bio-histories of Indigenous Caribbean peoples in the Lesser Antilles.

Mitochondrial DNA diversity of present-day Aboriginal Australians and implications for human evolution in Oceania.

Aboriginal Australians are one of the more poorly studied populations from the standpoint of human evolution and genetic diversity. Thus, to investigate their genetic diversity, the possible date of their ancestors' arrival and their relationships with neighboring populations, we analyzed mitochondrial DNA (mtDNA) diversity in a large sample of Aboriginal Australians. Selected mtDNA single-nucleotide polymorphisms and the hypervariable segment haplotypes were analyzed in 594 Aboriginal Australians drawn from locations across the continent, chiefly from regions not previously sampled. Most (~78%) samples could be assigned to mtDNA haplogroups indigenous to Australia. The indigenous haplogroups were all ancient (with estimated ages >40 000 years) and geographically widespread across the continent. The most common haplogroup was P (44%) followed by S (23%) and M42a (9%). There was some geographic structure at the haplotype level. The estimated ages of the indigenous haplogroups range from 39 000 to 55 000 years, dates that fit well with the estimated date of colonization of Australia based on archeological evidence (~47 000 years ago). The distribution of mtDNA haplogroups in Australia and New Guinea supports the hypothesis that the ancestors of Aboriginal Australians entered Sahul through at least two entry points. The mtDNA data give no support to the hypothesis of secondary gene flow into Australia during the Holocene, but instead suggest long-term isolation of the continent.

Genetic diversity in Svaneti and its implications for the human settlement of the Highland Caucasus.

OBJECTIVES: In this study, we characterized genetic diversity in the Svans from northwestern Georgia to better understand the phylogeography of their genetic lineages, determine whether genetic diversity in the highland South Caucasus has been shaped by language or geography, and assess whether Svan genetic diversity was structured by regional residence patterns. MATERIALS AND METHODS: We analyzed mtDNA and Y-chromosome variation in 184 individuals from 13 village districts and townlets located throughout the region. For all individuals, we analyzed mtDNA diversity through control region sequencing, and, for males, we analyzed Y-chromosome diversity through SNP and STR genotyping. The resulting data were compared with those for populations from the Caucasus and Middle East. RESULTS: We observed significant mtDNA heterogeneity in Svans, with haplogroups U1-U7, H, K, and W6 being common there. By contrast, ∼78% of Svan males belonged to haplogroup G2a, with the remainder falling into four other haplogroups (J2a1, I2, N, and R1a). While showing a distinct genetic profile, Svans also clustered with Caucasus populations speaking languages from different families, suggesting a deep common ancestry for all of them. The mtDNA data were not structured by geography or linguistic affiliation, whereas the NRY data were influenced only by geography. DISCUSSION: These patterns of genetic variation confirm a complex set of geographic sources and settlement phases for the Caucasus highlands. Such patterns may also reflect social and cultural practices in the region. The high frequency and antiquity of Y-chromosome haplogroup G2a in this region further points to its emergence there.

New native South American Y chromosome lineages.

Many single-nucleotide polymorphisms (SNPs) in the non-recombining region of the human Y chromosome have been described in the last decade. High-coverage sequencing has helped to characterize new SNPs, which has in turn increased the level of detail in paternal phylogenies. However, these paternal lineages still provide insufficient information on population history and demography, especially for Native Americans. The present study aimed to identify informative paternal sublineages derived from the main founder lineage of the Americas-haplogroup Q-L54-in a sample of 1841 native South Americans. For this purpose, we used a Y-chromosomal genotyping multiplex platform and conventional genotyping methods to validate 34 new SNPs that were identified in the present study by sequencing, together with many Y-SNPs previously described in the literature. We updated the haplogroup Q phylogeny and identified two new Q-M3 and three new Q-L54*(xM3) sublineages defined by five informative SNPs, designated SA04, SA05, SA02, SA03 and SA29. Within the Q-M3, sublineage Q-SA04 was mostly found in individuals from ethnic groups belonging to the Tukanoan linguistic family in the northwest Amazon, whereas sublineage Q-SA05 was found in Peruvian and Bolivian Amazon ethnic groups. Within Q-L54*, the derived sublineages Q-SA03 and Q-SA02 were exclusively found among Coyaima individuals (Cariban linguistic family) from Colombia, while Q-SA29 was found only in Maxacali individuals (Jean linguistic family) from southeast Brazil. Furthermore, we validated the usefulness of several published SNPs among indigenous South Americans. This new Y chromosome haplogroup Q phylogeny offers an informative paternal genealogy to investigate the pre-Columbian history of South America.Journal of Human Genetics advance online publication, 31 March 2016; doi:10.1038/jhg.2016.26.

Mitochondrial DNA and Y chromosome variation provides evidence for a recent common ancestry between Native Americans and Indigenous Altaians.

The Altai region of southern Siberia has played a critical role in the peopling of northern Asia as an entry point into Siberia and a possible homeland for ancestral Native Americans. It has an old and rich history because humans have inhabited this area since the Paleolithic. Today, the Altai region is home to numerous Turkic-speaking ethnic groups, which have been divided into northern and southern clusters based on linguistic, cultural, and anthropological traits. To untangle Altaian genetic histories, we analyzed mtDNA and Y chromosome variation in northern and southern Altaian populations. All mtDNAs were assayed by PCR-RFLP analysis and control region sequencing, and the nonrecombining portion of the Y chromosome was scored for more than 100 biallelic markers and 17 Y-STRs. Based on these data, we noted differences in the origin and population history of Altaian ethnic groups, with northern Altaians appearing more like Yeniseian, Ugric, and Samoyedic speakers to the north, and southern Altaians having greater affinities to other Turkic speaking populations of southern Siberia and Central Asia. Moreover, high-resolution analysis of Y chromosome haplogroup Q has allowed us to reshape the phylogeny of this branch, making connections between populations of the New World and Old World more apparent and demonstrating that southern Altaians and Native Americans share a recent common ancestor. These results greatly enhance our understanding of the peopling of Siberia and the Americas.

Oxytocin receptor gene sequences in owl monkeys and other primates show remarkable interspecific regulatory and protein coding variation.

The oxytocin (OT) hormone pathway is involved in numerous physiological processes, and one of its receptor genes (OXTR) has been implicated in pair bonding behavior in mammalian lineages. This observation is important for understanding social monogamy in primates, which occurs in only a small subset of taxa, including Azara's owl monkey (Aotus azarae). To examine the potential relationship between social monogamy and OXTR variation, we sequenced its 5' regulatory (4936bp) and coding (1167bp) regions in 25 owl monkeys from the Argentinean Gran Chaco, and examined OXTR sequences from 1092 humans from the 1000 Genomes Project. We also assessed interspecific variation of OXTR in 25 primate and rodent species that represent a set of phylogenetically and behaviorally disparate taxa. Our analysis revealed substantial variation in the putative 5' regulatory region of OXTR, with marked structural differences across primate taxa, particularly for humans and chimpanzees, which exhibited unique patterns of large motifs of dinucleotide A+T repeats upstream of the OXTR 5' UTR. In addition, we observed a large number of amino acid substitutions in the OXTR CDS region among New World primate taxa that distinguish them from Old World primates. Furthermore, primate taxa traditionally defined as socially monogamous (e.g., gibbons, owl monkeys, titi monkeys, and saki monkeys) all exhibited different amino acid motifs for their respective OXTR protein coding sequences. These findings support the notion that monogamy has evolved independently in Old World and New World primates, and that it has done so through different molecular mechanisms, not exclusively through the oxytocin pathway.

Y-chromosome analysis reveals genetic divergence and new founding native lineages in Athapaskan- and Eskimoan-speaking populations.

For decades, the peopling of the Americas has been explored through the analysis of uniparentally inherited genetic systems in Native American populations and the comparison of these genetic data with current linguistic groupings. In northern North America, two language families predominate: Eskimo-Aleut and Na-Dene. Although the genetic evidence from nuclear and mtDNA loci suggest that speakers of these language families share a distinct biological origin, this model has not been examined using data from paternally inherited Y chromosomes. To test this hypothesis and elucidate the migration histories of Eskimoan- and Athapaskan-speaking populations, we analyzed Y-chromosomal data from Inuvialuit, Gwich'in, and Tlich populations living in the Northwest Territories of Canada. Over 100 biallelic markers and 19 chromosome short tandem repeats (STRs) were genotyped to produce a high-resolution dataset of Y chromosomes from these groups. Among these markers is an SNP discovered in the Inuvialuit that differentiates them from other Aboriginal and Native American populations. The data suggest that Canadian Eskimoan- and Athapaskan-speaking populations are genetically distinct from one another and that the formation of these groups was the result of two population expansions that occurred after the initial movement of people into the Americas. In addition, the population history of Athapaskan speakers is complex, with the Tlich being distinct from other Athapaskan groups. The high-resolution biallelic data also make clear that Y-chromosomal diversity among the first Native Americans was greater than previously recognized.

Genetic diversity in Puerto Rico and its implications for the peopling of the Island and the West Indies.

Puerto Rico and the surrounding islands rest on the eastern fringe of the Caribbean's Greater Antilles, located less than 100 miles northwest of the Lesser Antilles. Puerto Ricans are genetic descendants of pre-Columbian peoples, as well as peoples of European and African descent through 500 years of migration to the island. To infer these patterns of pre-Columbian and historic peopling of the Caribbean, we characterized genetic diversity in 326 individuals from the southeastern region of Puerto Rico and the island municipality of Vieques. We sequenced the mitochondrial DNA (mtDNA) control region of all of the samples and the complete mitogenomes of 12 of them to infer their putative place of origin. In addition, we genotyped 121 male samples for 25 Y-chromosome single nucleotide polymorphism and 17 STR loci. Approximately 60% of the participants had indigenous mtDNA haplotypes (mostly from haplogroups A2 and C1), while 25% had African and 15% European haplotypes. Three A2 sublineages were unique to the Greater Antilles, one of which was similar to Mesoamerican types, while C1b haplogroups showed links to South America, suggesting that people reached the island from the two distinct continental source areas. However, none of the male participants had indigenous Y-chromosomes, with 85% of them instead being European/Mediterranean and 15% sub-Saharan African in origin. West Eurasian Y-chromosome short tandem repeat haplotypes were quite diverse and showed similarities to those observed in southern Europe, North Africa and the Middle East. These results attest to the distinct, yet equally complex, pasts for the male and female ancestors of modern day Puerto Ricans.

Mitochondrial genetic background modulates bioenergetics and susceptibility to acute cardiac volume overload.

Dysfunctional bioenergetics has emerged as a key feature in many chronic pathologies such as diabetes and cardiovascular disease. This has led to the mitochondrial paradigm in which it has been proposed that mtDNA sequence variation contributes to disease susceptibility. In the present study we show a novel animal model of mtDNA polymorphisms, the MNX (mitochondrial-nuclear exchange) mouse, in which the mtDNA from the C3H/HeN mouse has been inserted on to the C57/BL6 nuclear background and vice versa to test this concept. Our data show a major contribution of the C57/BL6 mtDNA to the susceptibility to the pathological stress of cardiac volume overload which is independent of the nuclear background. Mitochondria harbouring the C57/BL6J mtDNA generate more ROS (reactive oxygen species) and have a higher mitochondrial membrane potential relative to those with C3H/HeN mtDNA, independent of nuclear background. We propose this is the primary mechanism associated with increased bioenergetic dysfunction in response to volume overload. In summary, these studies support the 'mitochondrial paradigm' for the development of disease susceptibility, and show that the mtDNA modulates cellular bioenergetics, mitochondrial ROS generation and susceptibility to cardiac stress.