Extent of Germanic Admixture in Iberia and Italy

Extent of Germanic Admixture in Iberia and Italy

The recent study* on Y chromosome haplogroup I gives us the means to attempt a first-order quantification of the extent of Germanic admixture in parts of western Europe that were affected by the barbarian movements during and after the time of the western Roman empire's collapse.
Haplogroup I reaches high frequencies in the Germanic world, while its frequency in Italy and Iberia is low, making it an excellent candidate for this type of analysis. It is divided in three main clades:

• I1a originated in Franco-Cantabria and spread to northwestern Europe after the Last Glacial Maximum. Its maximum frequency today is in Norwegians (38.9%) and is frequent in Scandinavia and Germany (25%)
  
• I1b is divided into I1b2, frequent in Sardinia and Basque country, and undifferentiated I1b*, with a wide distribution and higher frequency, and a primary focus in the eastern Balkans (up to 40% in Bosnians). I1b* originated somewhere between the Adriatic and the Black Sea.
  
• I1c is correlated with I1a and shares a common haplotype with it, indicating a shared history of the two. Maximum frequency of 12.5% in Germans.
  

It should be stressed here that I originated in southern Europe and spread northwards after the LGM. But, given that today two particular clades (I1a+I1c) are very frequent among Germans compared to southern Europeans, we can hypothesize that any movement of Germanic speakers would introduce such chromosomes to the affected population.
I1a is found in Portuguese (1.3%), Catalans (3.1%), northern Italians (2.6%), central Italians (2%), Calabrians (0.7%), Italians of Albanian origin (1.3%), Italians from Apulia (1.3%). These numbers are less than 1/10 of the corresponding frequency in Germanic speakers.
I1c is found in Portuguese (1.6%), northern Italians (1%), central Italians (3%), Calabrians (1.4%), Italians of Albanian origin (3.8%), which are similarly less than 1/10 of the corresponding frequency.
In general, it appears that the introgression of Germanic elements into the Iberian and Italian peninsulas has been minimal. In particular, for the case of Italy where an "invigorating" Germanic admixture has been proposed by Teutonists as a cause of the Rennaissance and the economic prosperity of northern Italy, we observe that no such influence is observed.
While movements of peoples did in fact occur, causing the collapse of the western Empire, it appears that on the whole these did not alter the pre-existing genetic composition of the indigenous populations.

* Am. J. Hum. Genet., 75:000, 2004
Phylogeography of Y-Chromosome Haplogroup I Reveals Distinct Domains of Prehistoric Gene Flow in Europe
Siiri Rootsi
To investigate which aspects of contemporary human Y-chromosome variation in Europe are characteristic of primary colonization, late-glacial expansions from refuge areas, Neolithic dispersals, or more recent events of gene flow, we have analyzed, in detail, haplogroup I (Hg I), the only major clade of the Y phylogeny that is widespread over Europe but virtually absent elsewhere. The analysis of 1,104 Hg I Y chromosomes, which were identified in the survey of 7,574 males from 60 population samples, revealed several subclades with distinct geographic distributions. Subclade I1a accounts for most of Hg I in Scandinavia, with a rapidly decreasing frequency toward both the East European Plain and the Atlantic fringe, but microsatellite diversity reveals that France could be the source region of the early spread of both I1a and the less common I1c. Also, I1b*, which extends from the eastern Adriatic to eastern Europe and declines noticeably toward the southern Balkans and abruptly toward the periphery of northern Italy, probably diffused after the Last Glacial Maximum from a homeland in eastern Europe or the Balkans. In contrast, I1b2 most likely arose in southern France/Iberia. Similarly to the other subclades, it underwent a postglacial expansion and marked the human colonization of Sardinia 9,000 years ago.

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