Most males in modern Poland carry Y-chromosomal lineages from clades that have recently expanded over Central, Eastern and South-Eastern Europe.

Previous studies on Y-chromosomal haplogroup diversity in Poland have been focused mainly on macro-haplogroups. Consequently, younger subclades have rarely been explored to elucidate the relatively recent history of the Polish population. Here we present the results of deep genotyping of 598 chromosome Y sequences from modern Poland and demonstrate that about 60% of Polish males can be assigned to subhaplogroups that are both relatively young and widely distributed among different Slavic populations, thus supporting the scenario in which Early Slavic mass migration and territorial expansion took place in the first millennium of the common era. While most of those young Slavic-associated subclades are part of haplogroup R1a, other haplogroups, including I2a, R1b and E1b, are also represented by specific subclades, which together may constitute an important clue when trying to identify the location of the Proto-Slavic homeland based on ancient DNA data. Additionally, we have identified two specifically Polish subclades (I-Y6343 and R-Z17913, from haplogroups I1a and R1b, respectively) that likely descend from Late Ancient or Early Medieval founders representing the local Pre-Slavic population of the Roman period.