Haplogroup R1b-M269 comprises most Western European Y chromosomes; of its main branches, R1b-DF27 is by far the least known, and it appears to be highly prevalent only in Iberia. We have genotyped 1072 R1b-DF27 chromosomes for six additional SNPs and 17 Y-STRs in population samples from Spain, Portugal and France in order to further characterize this lineage and, in particular, to ascertain the time and place where it originated, as well as its subsequent dynamics. We found that R1b-DF27 is present in frequencies ~40% in Iberian populations and up to 70% in Basques, but it drops quickly to 6–20% in France. Overall, the age of R1b-DF27 is estimated at ~4,200 years ago, at the transition between the Neolithic and the Bronze Age, when the Y chromosome landscape of W Europe was thoroughly remodeled. In spite of its high frequency in Basques, Y-STR internal diversity of R1b-DF27 is lower there, and results in more recent age estimates; NE Iberia is the most likely place of origin of DF27. Subhaplogroup frequencies within R1b-DF27 are geographically structured, and show domains that are reminiscent of the pre-Roman Celtic/Iberian division, or of the medieval Christian kingdoms.

The dissection of S116 in more than 1500 individuals from Atlantic Europe and the Iberian Peninsula has provided important clues about the controversial evolutionary history of M269. First, the results do not point to an origin of M269 in the FrancoCantabrian refuge, owing to the lack of sublineage diversity within M269, which supports the new theories proposing its origin in Eastern Europe. Second, S116 shows frequency peaks and spatial distribution that differ from those previously proposed, indicating an origin farther west, and it also shows a high frequency in the Atlantic coastline. Third, an outstanding frequency of the DF27 sublineage has been found in Iberia, with a restricted distribution pattern inside this peninsula and a frequency maximum in the area of the Franco-Cantabrian refuge. This entire panorama indicates an old arrival of M269 into Western Europe, because it has generated at least two episodes of expansion in the Franco-Cantabrian area. This study demonstrates the importance of continuing the dissection of the M269 lineage in different European populations because the discovery and study of new sublineages can adjust or even completely revise the theories about European peopling, as has been the case for the place of origin of M269.

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Single-nucleotide polymorphisms (SNPs) found within the non-recombining region of the Y chromosome (NRY) represent a powerful tool in forensic genetics for inferring the paternal ancestry of a vestige and complement the determination of biogeographical origin in combination with other markers like AIMs. In the present study, we introduce a panel of 15 Y-SNPs for a fine-resolution subtyping of the haplogroup R1b-DF27, in a single minisequencing reaction. This is the first minisequencing panel that allows a fine subtyping of R1b-DF27, which displays high frequencies in Iberian and Iberian-influenced populations. This panel includes subhaplogroups of DF27 that display moderate geographical differentiation, of interest to link a sample with a specific location of the Iberian Peninsula or with Iberian ancestry. Conversely, part of the intricacy of a new minisequencing panel is to have all the included variants available to test the effectiveness of the analysis method. We have overcome the absence of the least common variants through site-directed mutagenesis. Overall, the results show that our panel is a robust and effective method for subtyping R1b-DF27 lineages from a minimal amount of DNA, and its high resolution enables to improve male lineage discrimination in Iberian and Southwest European descent individuals. The small length of the amplicons and its reproducibility makes this assay suitable for forensic and population genetics purposes.

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