Haplogroup I (Y-DNA)

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In human genetics, Haplogroup I (M170) is a Y-chromosome haplogroup.

Haplogroup I (pronounced "eye") appears to be native to Europe. Its initial spread is believed to be connected to migrations of people during the last glacial maximum (LGM). It can be found in most European populations, most commonly in Scandinavia, Sardinia, Croatia, and Bosnia. Haplogroup I Y-chromosomes have also been found among some populations of the Middle East, the Caucasus, and Central Asia, but they are found at frequencies exceeding 10% only among populations of Europe and Asia Minor, particularly among Germanic, Celtic, Slavic, Uralic, and Turkic peoples, as well as among the Romance-speaking populations of France, Romania, Moldova, and Sardinia, the Albanian-speaking population of Albania, and the Greek-speaking population of Greece. Within Europe, several populations are distinguished by having a significantly lower frequency of Haplogroup I than the surrounding populations: these depressions in the frequency of Haplogroup I distinguish the populations of Italy and Switzerland from Germany and Sardinia, Iberia from southern France and Normandy, Greece from Albania and the Slavic peoples, and the Baltic Latvians from the Finnic Estonians. Thus, it could be said that Haplogroup I displays relatively higher frequencies among peoples who have at times been considered to be "northern barbarians." The great majority of the Y-chromosomes among even these "northern barbarians," however, is comprised of the same haplogroups (R1b in Western Europe, R1a1 in Eastern Europe, and N in Northeastern Europe) as the majority of the Y-chromosomes of the southerly, earlier civilized populations.

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[edit] Origins

Haplogroup I is most closely related to Haplogroup J, as both Haplogroup I and Haplogroup J are descendants of Haplogroup IJ (S2, S22). Haplogroup IJ is in turn derived from Haplogroup F.

According to current theories, Haplogroup I first arrived in Europe around 20,000-25,000 years ago from the Middle East. It is believed to be associated with the Gravettian culture. [1] Although Haplogroup I occurs at only very low frequencies among modern populations of the Middle East and Caucasus, some of its oldest branches, which are classified as Haplogroup I*, have been found among the populations of Turkey (8/741), Adygea (2/138), and Iraq (1/176). Overall, the highest frequencies of Haplogroup I* appear to be found among the Andalusians (3/103), French (4/179), Slovenians (2/55), and the Saami (1/35).

At present, the highest frequencies of Haplogroup I can be found in Scandinavia, Sardinia and Croatia. The Haplogroup I Y-chromosomes found among the Scandinavians, Sardinians, and Slavs generally belong to different subclades, however, which indicates that each of the ancestral populations bearing a particular subclade experienced an independent population expansion. Nearly all the Haplogroup I Y-chromosomes among Scandinavians (including both Germanic and Uralic peoples of the region) belong to the subclade I1a (M253, M307, P30, P40), which is also found at moderate frequencies throughout the rest of Europe. One characteristic of the Scandinavian I1a Y-chromosomes is their rather low haplotype diversity: a greater variety of Haplogroup I1a Y-chromosomes has been found among the French and Italians, despite the much lower overall frequency of Haplogroup I1a among the modern French and Italian populations, which suggests that the Haplogroup I element of the ancestry of Scandinavians might be descended from a very small Paleolithic population of Southern European extraction. The Haplogroup I Y-chromosomes that comprise more than 40% of all patrilines among the Sardinians, however, belong almost exclusively to the peculiar Haplogroup I1b1b (M26), which is found outside of Sardinia only at low frequencies in Southwest Europe; Haplogroup I1b2, a typically Saxon haplogroup, also occurs among approximately 1% of Sardinians. The Haplogroup I component of the Y-chromosome diversity of Eastern European populations consists mainly of Haplogroup I1b1*, which reaches its peak frequency among Bosnians and Croats, although the typically Scandinavian Haplogroup I1a is also found throughout Eastern Europe at a moderate frequency but with rather high haplotype diversity.

The high frequency and diversity of Haplogroup I1b1* (P37.2) among populations of the Western Balkans lends support to the hypothesis that the Adriatic region of modern-day Croatia served as a refuge for populations bearing Haplogroup I1b1* during the last glacial maximum. These groups seem to be the ancestors of about 38% of modern day Croats (75% of Bosnian Croats).

Another Paleolithic population of Europe seems to have weathered the last ice age in a refuge located somewhere in the Iberian Peninsula or southern France, or perhaps the Italian Peninsula; after the end of the ice age, some of them headed northward and repopulated Northwest Europe and Scandinavia. This population appears to have carried haplogroups I1a and I1b2 at significant frequencies, with a numerical superiority of Haplogroup I1a. Their descendants are primarily found among the Germanic, Uralic, and Celtic populations of Northern Europe, although almost always overshadowed by the more prevalent carriers of Haplogroup R or Haplogroup N. Haplogroup I1a displays a very clear frequency gradient, with a peak frequency of approximately 35% among the populations of southern Norway, southwestern Sweden, and Denmark, and rapidly decreasing frequencies toward the edges of the historically Germanic-influenced world. However, measures of intra-haplogroup diversity (STR diversity) of I1a Y-chromosomes are highest among the French and the Italians, followed closely by the Swedes, Estonians, and Hungarians, which suggests that Haplogroup I1a may have been harbored by two distinct Paleolithic European populations, one inhabiting southern France or the Italian Peninsula and the other inhabiting some ice age refuge in Eastern Europe that was perhaps separate from the Balkan refuge that harbored Haplogroup I1b1*. The distribution of Haplogroup I1b2 is closely correlated to that of Haplogroup I1a except in Fennoscandia, which suggests that it was probably harbored by at least one of the Paleolithic refuge populations that also harbored Haplogroup I1a; the lack of correlation between the distributions of I1a and I1b2 in Fennoscandia may be a result of Haplogroup I1b2's being more strongly affected by founder effects and genetic drift due to its rarity, as Haplogroup I1b2 comprises less than 10% of the total Y-chromosome diversity of all populations outside of Lower Saxony. Haplogroup I1b2 has been found in over 4% of the population only in Germany, the Netherlands, Belgium, Denmark, England (not including Wales or Cornwall), Scotland, and the southern tips of Sweden and Norway in Northwest Europe; the provinces of Normandy, Maine, Anjou, and Perche in northwestern France; the province of Provence in southeastern France; the regions of Tuscany, Umbria, and Latium in Italy; and Moldavia and the area around Russia's Ryazan Oblast and Republic of Mordovia in Eastern Europe. One subclade of Haplogroup I1b2, namely I1b2a1 (M284), has been found almost exclusively among the population of Great Britain, which has been taken to suggest that the clade may have a very long history in that island. It is notable, however, that the distributions of Haplogroup I1a and Haplogroup I1b2 seem to correlate fairly well with the extent of historical influence of Germanic peoples, although the punctual presence of both haplogroups at a low frequency in the area of the historical regions of Bithynia and Galatia in Turkey rather suggests a connection with the ancient Gauls of Thrace, several tribes of which are recorded to have immigrated to those parts of Anatolia at the invitation of Nicomedes I of Bithynia.

A distinct Western European Paleolithic population that bore Haplogroup I1b1b (M26) must have existed somewhere west of the Apennines in eastern Iberia, southern France, or western Italy, from which it succeeded in the first substantial colonization of the island of Sardinia approximately 9,000 years ago. Despite the fact that the predominantly Sardinian Haplogroup I1b1b-M26 is derived from the predominantly Balkan Haplogroup I1b1*-P37.2, the derived Haplogroup I1b1b is practically absent east of France and Italy, while it is found at low but significant frequencies outside of Sardinia in the Balearic Islands, Castile, the Basque Country, the Pyrenees, southern and western France, and parts of the Maghreb, Great Britain, and Ireland. Thus, Haplogroup I1b1b appears to be strongly associated with Southwest Europeans of Paleolithic ancestry, and its carriers bear only a distant relictual relationship to the I1b1*-bearing populations of the Balkans. It is also interesting that, although the distributions of Haplogroup I1b1b and the predominantly Scandinavian Haplogroup I1a overlap in parts of western France and the British Isles, and both haplogroups appear to have a very long history in Southwest Europe (and particularly France), the populations bearing these two haplogroups appear to have differentiated at a very early date and have not extensively mixed since that time. Haplogroup I1b1b appears to be the only subclade of Haplogroup I found among the Basques, although subclades of Haplogroup R1b comprise the vast majority of that people's Y-chromosome diversity. It is notable that Haplogroup I1b1b appears to be found at somewhat higher frequencies among the general populations of Castile in Spain and Béarn in France than among the population of ethnic Basques.

There are also indications that Haplogroup I, or at least certain subclades of it, might be tied to the Celtic culture. The spread of Haplogroup I in Western Europe could be consistent with the Celtic expansion that occurred in the mid-first millennium BC; in this case, it is likely that Haplogroup I was not a haplogroup of the original Celtic people, but rather became associated with their descendants after they had absorbed many of the Paleolithic inhabitants of Central and Western Europe.


Recently (Rootsi et al. 2004), haplogroup I was divided into several subclades that show unique distribution in certain parts of Europe.


Subclade I1a (M253, M307) is present especially in Scandinavia, with a moderate distribution throughout Northwest Europe and Eastern Europe. Of the subclades of the other major branch of Haplogroup I, the potentially paraphyletic I1b1* (P37) is prevalent in the Dinaric Alps, while a subclade of I1b1, I1b1b (M26), makes up the largest percentage of Y-chromosome haplogroups in Sardinia. Another subclade of the I1b branch, I1b2a (M223), is found at a rather low frequency among populations of Northwest Europe. More work is needed to elucidate the relationships between the subclades of Haplogroup I and the migration processes in which bearers of subclades of Haplogroup I took part.



[edit] Subgroups

The subclades of Haplogroup I with their defining mutation, according to the 2006 ISOGG tree:

  • I (M170, M258, P19)
    • I*
    • I1 (P38)
      • I1*
      • I1a (M253, M307, P30, P40) Typical of populations of Scandinavia and Northwest Europe, with a moderate distribution throughout Eastern Europe
        • I1a*
        • I1a1 (M227) Appears to be limited to a marginally low frequency of approximately 1% among Slavic and Uralic peoples of Eastern Europe; also detected in a single Lebanese man
        • I1a2 (M21)
        • I1a3 (M72)
      • I1b (S31)
        • I1b*
        • I1b1 (P37.2) Typical of the South Slavic peoples of the Balkans, especially the populations of Bosnia and Croatia; also found with high haplotype diversity values, but lower overall frequency, among the West Slavic populations of Slovakia and the Czech Republic; a node of elevated frequency in Moldavia correlates with that observed for Haplogroup I1b2 (but not for Haplogroup I1a)
          • I1b1*
          • I1b1a (P41.2 (M359.2))
          • I1b1b (M26) Typical of the population of the so-called "archaic zone" of Sardinia; also found at low frequencies among populations of Southwest Europe, particularly in Castile, Béarn, and the Basque Country
            • I1b1b*
            • I1b1b1 (M161)
        • I1b2 (S23, S30, S32, S33) Occurs at a moderate frequency among populations of Northwest Europe, with a peak frequency in the region of Lower Saxony in central Germany; minor offshoots appear in Moldavia and Russia (especially around Vladimir, Ryazan, Nizhny Novgorod, and the Republic of Mordovia)
          • I1b2*
          • I1b2a (M223, S24)
            • I1b2a*
            • I1b2a1 (M284) Generally limited to a low frequency in Great Britain
            • I1b2a2 (M379)
            • I1b2a3 (P78)
            • I1b2a4 (P95)

[edit] References

[edit] External links

Human Y-chromosome DNA (Y-DNA) haplogroups
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