Maybe now someone should write a similar study about aDNA from Ancient Lithuania and Latvia.
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Sile, in the link you provided there is this info:
Maybe we will also learn what was the Y-DNA haplogroup of the Piast clan.
I suspect that it could be so called "type P" of R1a L260, which - according to Peter Gwozdz - is about 1100 - 2400 years old (most likely 1600 years old) and can be found among around 9% (7% to 11%) of people in Poland. L260 as such is older - between 2500 and 3100 years old - but so called "type P" (which is found in large frequencies in Poland, in one region of Slovakia near the Polish border called Zamagurie and in some parts of the Czech Republic) is younger.
In Ireland about 8% of males have Y-DNA of the Uí Néill clan, established by Niall of the Nine Hostages (who lived by the end of the 4th century AD). His clan dominated Ireland from 5th to 10th centuries. In Northern Ireland the % of this haplotype is even higher - up to 21%.
About Niall of the Nine Hostages:
http://www.irishcentral.com/roots/niall-took-no-hostages-43038522-237784201.html
The Piast clan was probably already numerous when Mieszko I lived (for example we know from sources that Mieszko had several brothers - one of them was Czcibor - brothers helped him in ruling the country; Mieszko also had several Pagan wifes before he become Christianized, he probably had sons with those wifes - they probably later became governors of provinces such as Mazovia or Pomerania, high-ranking officials, commanders of units, etc. - I think it could be a family business and strong
nepotism could be the case).
If "type P" of L260 is not "Piast marker", then maybe it is "Lech marker" (maybe "Lechites" are "sons of Lech").
Provided of course that Lech really existed and was really called Lech.
If his real name was not Lech, then maybe let's call him "Y-chromosomal Lech", like they did with Adam.
Here is the website of Peter Gwozdz where he discusses L260 and other clades:
http://www.gwozdz.org/polishclades.html
http://www.gwozdz.org/PolishClades.html#PType
https://www.facebook.com/R1aM458/posts/152294778301448
L260 is a subclade of M458, but for example L365 is a subclade of Z280 and it also seems to be very Polish-specific:
L365 is about 2500 - 3300 years old:
https://www.familytreedna.com/public/r1a/default.aspx?section=results
Gwozdz calls it "type G":
http://www.gwozdz.org/PolishClades.html#GType
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When it comes to Iron Age DNA, see also this link (and comments below):
http://polishgenes.blogspot.com.au/2012/06/first-direct-evidence-of-genetic.html