Haplogroup I is a descendant (subclade) of haplogroup N1a1b and sibling of haplogroup N1a1b1 (Olivieri 2013). It is believed to have arisen somewhere in West Asia between 17,263 and 24,451 years before present (BP) (Behar 2012b), with coalescence age of 20.1 thousand years ago (Olivieri 2013). It has been suggested that its origin may be in Iran or more generally the Near East (Terreros 2011). It has diverged to at least seven distinct clades i.e. branches I1-I7, dated between 16-6.8 thousand years (Olivieri 2013). The hypothesis about its Near Eastern origin is based on the fact that all haplogroup I clades, especially those from Late Glacial period (I1, I4, I5, and I6), include mitogenomes from the Near East (Olivieri 2013). The age estimates and dispersal of some subclades (I1, I2’3, I5) are similar to those of major subclades of the mtDNA haplogroups J and T, indicating possible dispersal of the I haplogroup into Europe during the Late Glacial period (c. 18–12 kya) and postglacial period (c. 10–11 kya), several millennia before the European Neolithic period. Some subclades (I1a1, I2, I1c1, I3) show signs of the Neolithic diffusion of agriculture and pastoralism within Europe (Olivieri 2013).
It is noteworthy that, with the exception of its northern neighbor Azerbaijan, Iran is the only population in which haplogroup I exhibits polymorphic levels. Also, a contour plot based on the regional phylogeographic distribution of the I haplogroup exhibits frequency clines consistent with an Iranian cradle ... Moreover, when compared with other populations in the region, those from the Levant (Iraq, Syria and Palestine) and the Arabian Peninsula (Oman and UAE) exhibit significantly lower proportions of I individuals ... this haplogroup has been detected in European groups (Krk, a tiny island off the coast of Croatia (11.3%), and Lemko, an isolate from the Carpathian Highlands (11.3%)) at comparable frequencies to those observed in the North Iranian population. However, the higher frequencies of the haplogroup within Europe are found in geographical isolates and are likely the result of founder effects and/or drift ... it is plausible that the high levels of haplogroup I present in Iran may be the result of a localized enrichment through the action of genetic drift or may signal geographical proximity to the location of origin.
Haplogroup I ... dates to ∼25 ka ago and is overall most frequent in Europe ..., but the facts that it has a frequency peak in the Gulf region and that its highest diversity values are in the Gulf, Anatolia, and southeast Europe suggest that its origin is most likely in the Near East and/or Arabia ...
The highest frequencies of mitochondrial haplogroup I observed so far appear in the Cushitic-speaking El Molo (23%) and Rendille (>17%) in northern Kenya (Castrì 2008). The clade is also found at comparable frequencies among the Soqotri (~22%).
Haplogroup I is present across West Asia and Central Asia, and is also found at trace frequencies in South Asia. Its highest frequency area is perhaps in northern Iran (9.7%). Terreros 2011 notes that it also has high diversity there and reiterates past studies that have suggested that this may be its place of origin. Found in Svan population from Georgia(Caucasus) I* 4.2%."Sequence polymorphisms of the mtDNA control region in a human isolate: the Georgians from Swanetia."Alfonso-Sánchez MA1, Martínez-Bouzas C, Castro A, Peña JA, Fernández-Fernández I, Herrera RJ, de Pancorbo MM. The table below shows some of the populations where it has been detected.
In Western Europe, haplogroup I is most common in Northwestern Europe (Norway, the Isle of Skye, and the British Isles). The frequency in these areas is between 2 and 5 percent. Its highest frequency in Brittany, France where it is over 9 percent of the population in Finistère. It is uncommon and sometimes absent in other parts of Western Europe (Iberia, South-West France, and parts of Italy).
In Eastern Europe, the frequency of haplogroup I is generally lower than in Western Europe (1 to 3 percent), but its frequency is more consistent between populations with fewer places of extreme highs or lows. There are two notable exceptions. Nikitin 2009 found that Lemkos (a sub- or co-ethnic group of Rusyns) in the Carpathian mountains have the "highest frequency of haplogroup I (11.3%) in Europe, identical to that of the population of Krk Island (Croatia) in the Adriatic Sea".[Footnote 1][Footnote 2]
Haplogroup I has until recently been absent from ancient European samples found in Paleolithic and Mesolithic grave sites. In 2017, in a site on Italian island of Sardinia was found a sample with the subclade I3 dated to 9124-7851 BC (Modi 2017), while in the Near East, in Levant was found a sample with yet-not-defined subclade dated 8,850-8,750 BC, while in Iran was found a younger sample with subclade I1c dated to 3972-3800 BC (Lazaridis 2016). In Neolithic Spain (c. 6090-5960 BC in Paternanbidea, Navarre) was found a sample with yet-not-defined subclade (Olivieri 2013). Haplogroup I displays a strong connection with the Indo-European migrations; especially its I1, I1a1 and I3a subclades, which have been found in Poltavka and Srubnaya cultures in Russia (Mathieson 2015), among ancient Scythians (Der Sarkissian 2011), and in Corded Ware and Unetice Culture burials in Saxony (Brandt 2013). Haplogroup I (with undetermined subclades) has also been noted at significant frequencies in more recent historic grave sites (Melchior 2008 and Hofreiter 2010).
In 2013, Nature announced the publication of the first genetic study utilizing next-generation sequencing to ascertain the ancestral lineage of an Ancient Egyptian individual. The research was led by Carsten Pusch of the University of Tübingen in Germany and Rabab Khairat, who released their findings in the Journal of Applied Genetics. DNA was extracted from the heads of five Egyptian mummies that were housed at the institution. All the specimens were dated to between 806 BC and 124 AD, a time frame corresponding with the Late Dynastic and Ptolemaic periods. The researchers observed that one of the mummified individuals likely belonged to the I2 subclade. Haplogroup I has also been found among ancient Egyptian mummies excavated at the Abusir el-Meleq archaeological site in Middle Egypt, which date from the Pre-Ptolemaic/late New Kingdom, Ptolemaic, and Roman periods.
We have previously observed a high frequency of Hg I's among Iron Age villagers (Bøgebjerggård) and individuals from the early Christian cemetery, Kongemarken , . This trend was also found for the additional sites reported here, Simonsborg, Galgedil and Riisby. The overall frequency of Hg I among the individuals from the Iron Age to the Medieval Age is 13% (7/53) compared to 2.5% for modern Danes . The higher frequencies of Hg I can not be ascribed to maternal kinship since only two individuals share the same common motif (K2 and K7 at Kongemarken). Except for Skovgaarde (no Hg I's observed) frequencies range between 9% and 29% and there seems to be no trend in relation to time. No Hg I's were observed at the Neolithic Damsbo and the Bronze Age site Bredtoftegård, where all three individuals harbored Hg U4 or Hg U5a (Table 1).
The frequency of haplogroup I may have undergone a reduction in Europe following the Middle Ages. An overall frequency of 13% was found in ancient Danish samples from the Iron Age to the Medieval Age (including Vikings) from Denmark and Scandinavia compared to only 2.5% in modern samples. As haplogroup I is not observed in any ancient Italian, Spanish [contradicted by the recent research as have been found in pre-Neolithic Italy as well Neolithic Spain], British, central European populations, early central European farmers and Neolithic samples, according to the authors "Haplogroup I could, therefore, have been an ancient Southern Scandinavian type "diluted" by later immigration events" (Hofreiter 2010).
It formed during the Last Glacial pre-warming period. It is found mainly in Europe, Near East, occasionally in North Africa and the Caucasus.
It is the most frequent clade of the haplogroup (Olivieri 2013).
It is the common root clade for subclades I2 and I3. There's a sample from Tanzania with which I2'3 shares a variant at position 152 from the root node of haplogroup I, and this "node 152" could be upstream I2'3s clade (Olivieri 2013). Both I2 and I3 might have formed during the Holocene period, and most of their subclades are from Europe, only few from the Near East (Olivieri 2013). Examples of this ancestral branch have not been documented.
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