This finding suggests that the I1b*(xM26) lineages might have expanded from SEE to central, eastern and southern Europe, presumably not earlier than the YD to Holocene transition and not later than the early Neolithic.
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Although present level of phylogenetic resolution does not allow further subdivision of this haplogroup by binary markers, based on strong geographic structuring of diverse microsatellite motifs, E3b-M78 is suggested to be a collection of subclades with different evolutionary histories (Cruciani et al. 2004, Semino et al. 2004) out of which the α cluster, largely characterized by an A7.1 nine-repeat allele, is confined to Europe (the Balkans) and Turkey (Cruciani et al. 2004)

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In Europe the highest E3b1α variance is among Apulians, Greeks and Macedonians and the highest frequency of the cluster is among Albanians, Macedonians and Greeks (table 1). Bearing in mind the congruent E3b1α frequency, variance maximums and star-like phylogenetic network (fig. 8B), it is possible to envision that a yet undefined sublineage downstream of M78, characterized by the nine-repeat allele at A7.1 locus, may have originated in south and southeastern Europe from where it dispersed in different directions.
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These observations hint a mosaic of different E3b1 dispersal modes over a short geographic distance and point to the Vardar-Morava- Danube river system as one of major routes for E3b1, in fact E3b1α, expansion from south and southeastern to continental Europe. In fact, dispersals of farmers throughout the Vardar-Morava- Danube catchments basin are also evidenced in archeological record (Taringham, 2000).

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R1a haplogroup occurs at 16% frequency in SEE (fig. 2). The age of M17 has been approximated to 15 KYA (Semino et al. 2000, Wells et al. 2001). Kivisild et al. (2003) suggested that southern and western Asia might be the source of R1 and R1a differentiation.

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Current R1a- M17/SRY-1532 distribution in Europe shows an increasing west-east frequency and variance gradients with peaks among Finno-Ugric and Slavic speakers (figs. 5C and 5D). Similarly to I1b* (xM26), R1a frequency gradient decreases slowly to the south (to 10% in Albanians, 8% in Greeks and 7% in Turks) and abruptly in the west (3% in Italians) (table 1). R1a frequency and STR variance decrease in the north-south direction in SEE, from 34% - 25% in mainland Croatians and Bosnians to 12% - 16% in Herzegovinians, Macedonians and Serbians (figs. 5A and 5B).

[...]

At this level of resolution it is not clear what temporal and effective population size differences contributed to this deep Paleolithic signal as high R1a variance in SEE might be explained by either ancient emography or more recent bottlenecks and founder effects in different Slavic tribes. At least three major episodes of gene flow might have enhanced R1a variance in the region: early post-LGM recolonizations expanding from the refugium in Ukraine, migrations from northern Pontic steppe between 3000 to 1000 B.C. as well as possibly massive Slavic migration from 5th to 7th AD.

taken from:
Episodes of Paternal Gene Flow Among Slavic Populations