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Wednesday, March 21, 2007

mtDNA Haplogroup U3

Because of the tremendous genetic diversity in Italy, our project sometimes accumulates a group of folks that would be hard to find elsewhere.

One example is the proportion of mtDNA haplogroup U3 in our project. At nearly 5% of our mtDNA results, U3 is nearly ten times as heavily represented in our project as in mitosearch, for example. Because U3 is not very well studied, I was asked by one of our members to look into it. Here's some of what I found.

Haplogroup U3 is a subclade of haplogroup U, and can be distinguished by two commonly reported markers: 16343G (in HVR1) and 150T (in HVR2). In addition, there are two coding region markers (14139G and 15454C) which seperate U3 from other subclades of U.

Moreover, there are two common subclades of U3. U3a is defined by seven coding region markers and and by the HVR1 marker 16390A. U3b is defined by four different coding region markers (and the absence of 16390A, of course). U3a almost always has the HVR1 marker 16519C as well.

By convention HVR1 results are sometimes reported without the 16000 prefix, so U3b usually has HVR1 results of simply 343G and U3a usually has 343G, 390A, and 519C.

U3 is found at the highest frequency among populations around the Black Sea (e.g Bulgaria and Georgia), but is found throughout Europe. It most likely spread from the Caucusas as part of Neolithic expansion into Europe along the Danube River basin, as the map on the right suggests (click here for a printable version).

U3 (especially U3b) is also found at very high levels among some European Roma populations, likely due to a particularly strong founder effect. U3 is also found throughout the Near East and in North Africa.

So why is U3 disproportionately common in Italy, especially in Sicily? One possibility is that the Neolithic expansion that brought U3 into Europe was particularly successful in Italy. Another possibility is that U3, especially U3b, came to Italy with the Roma people in historic times. Additionally, U3 was likely present among many other peoples that had contact with Italy over the millenia (Phonecians, Byzantines, etc.). Perhaps, with more research and further testing, a more accurate picture of U3 will be forthcoming.

2 Comments:

Blogger Bismarck said...

I just want to point out, that as Walter Pitman & William Ryan have shown, in their book "Noah's Flood", the Black Sea hadn't flooded to its present size until ~5600 BC. Before then, it was a much smaller freshwater lake, and the Caspian Sea had an arm jutting out northwest-ward.

Given that the Neolithic expansion around the Black Sea began by 7000 BC, this could have some relevance.

11:44 PM  
Blogger LadyAlaise said...

Very interesting! I am not a member of the Italy DNA project but I am a member of the Ireland mtDNA project as my maternal line goes right to Ireland (I'm 4th Generation Irish American). I only did the HVR1 and HVR2 tests; I haven't done the coding region yet but based on my current matches; most are U3 (as I am) or U3a1c. I have the 16343G and 150T markers and I have the HVR1 marker (compared to rCRS) 16519C. I am rather frustrated that there isn't much 'out there' about U3 in general aside from short and vague descriptions and barely anything on further subclades of U3.
Your blog is one of the more informative sources I have come across.
Thank you!

11:59 PM  

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