Contemporary human mtDNA haplogroup distribution, based on analysis of 2,054 individuals from 26 populations. (a) Pie charts on the map. (b) Counts of haplogroups in table format. For populations details, see 1000 Genomes Project#Human genome samples.
Mitochondria are the primary energy generator of the cell and have its unique organelles that maintain their own DNA (mtDNA). In human genetics, human mitochondrial DNA haplogroups are collections of similar haplotypes defined by combinations of single nuclear polymorphism (SNPs) in mtDNA inherited from a common ancestor[2]. Mitochondrial DNA is passed down through cytoplasmic inheritance, where, upon fertilization, the paternal mitochondria are degraded, leaving only the maternal mitochondria regardless of the offspring’s sex[3]. This characteristic of mitochondrial inheritance allows geneticists to track the movement and divergence of different haplogroups from female lineages. Haplogroups are used to represent the major branch points on the mitochondrial phylogenetic tree. Understanding this mechanism of inheritance has helped population geneticists trace the matrilineal inheritance of modern humans back to human origins in Africa and the subsequent spread around the globe.
The letter names of the haplogroups (not just mitochondrial DNA haplogroups) run from A to Z. As haplogroups were named in the order of their discovery, the alphabetical ordering does not have any meaning in terms of actual genetic relationships.
The rate at which mitochondrial DNA mutates is known as the mitochondrial molecular clock. It is an area of ongoing research with one study reporting one mutation per 8000 years.[4]
Recent research has shown that mitochondrial DNA haplogroups can influence risk for various diseases and cancers[5].
mtDNA haplogroup tree and distribution map. The numbers are haplogroup labels, reported according to the http://www.phylotree.org/ nomenclature, and give the location of one of the mutations leading to the derived haplotype. (Only a single branch defining marker, preferably from the coding region, is shown.) The main geographic features of haplogroup distribution are highlighted with colour.Chart showing the evolution of mitochondrial DNA Haplogroups to MRCA.Dispersal route of human mtDNA haplogroups
This phylogenetic tree is based Van Oven (2009).[7] In June 2022, an alternative phylogeny for haplogroup L was suggested[8]
Estimated world map of human migrations based on mtDNA haplogroups.
Macro-haplogroup L
Macro-haplogroup L is the most basal of human mtDNA haplogroups, from which all other haplogroups descend (specifically, from haplogroup L3). These haplogroups represent the majority of the typical sub-Saharan mtDNA variability. Approximately 65% of the European L lineages mostly likely arrived during the Arab conquest of Iberian Peninsula and Sicily and during the period of Atlantic slave trade. The remaining 35% of L mtDNAs form European-specific subclades, revealing that the gene flows from sub-Saharan Africa toward Europe from 11,000 years ago[9].
Macro-haplogroup H is found mostly in Europeans countries, clearly dominates the mitochondrial gene pool by occupying ~40-45% . Its focus has been an important aspect of human genetic diversity studies for more than a decade. Examining the spatial distribution of H lineage and other feature associated with its evolutionary history can reveal the formation of the western European gene pool. It is estimated that the coalescence time for Hg H is ~21,000 years ago, which led to the proposal that the clade was involved in a post-glacial population re-expansion from southwestern Europe to the rest of the continent . Most of the population along the westernmost Mediterranean coasts, separated by a narrow body of water, show the highest frequencies of mitochondrial haplogroup H. The most basal nodes of the most frequent H sub-haplogroup, H1 and H3, harbored many individuals of western Europe origins (primarily Iberian and Maghrebian regions).
There has been recent research into the regional and temporal development of haplogroup H in Europe. A 2017 study published in BMC Genomic Data analyzed mitochondrial DNA haplogroup H in 750 individuals from southern Spain, finding 337 carriers primarily from the Andalusian provinces of Huelva and Granada[10]. The research revealed that both populations exhibited a predominantly western European genetic profile, though Granada showed additional affinities with eastern Mediterranean populations, suggesting historical gene flow. Sub-haplogroups H1 and H3 were the most common, with molecular dating indicating origins around 16,000 and 13,000 years ago, respectively, and shared ancestry between Iberian and North African groups. Significant haplotype sharing between Andalusia and Morocco pointed to the Strait of Gibraltar as a corridor for maternal gene exchange rather than a genetic barrier. Overall, haplogroup H frequencies of about 39% in Huelva and 48% in Granada highlighted local diversity shaped by post-glacial expansions and later trans-Mediterranean interactions.
A 2004 paper suggested that the haplogroups most common in modern West Asian, North African and European populations were: H, J, K, N1, T, U4, U5, V, X and W.[12]
↑ Kim, Dong-han; Kim, Kijeong; Kim, Kyung-yong; Kim, Yoonyeong; Kwon, Chulhwan (2020-04-23). "Haplotracker: a web application for simple and accurate mitochondrial haplogrouping using short DNA fragments". bioRxiv10.1101/2020.04.23.057646v1.
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