MJ network of Y chromosomes from men with Uí Néill–derived surnames. The sample population (n=59) features the IMH as its modal haplotype, which is ancestral to a phylogenetically coherent cluster (blackened circles) that accounts for over half (52.5%) of the sample group. The cluster was taken to extend to all haplotypes that could be continuously traced to the ancestral IMH Y chromosome via a pathway of increasing frequency, a topology roughly in line with expectations under a Poisson-distributed mutational process.

Phylogeography of the IMH Y-chromosome lineage. A, Contour map displaying the frequency distribution of the IMH. It shows a clear focus on northwestern areas of the island, where it reaches a regional maximum of 16.9% (21.5% including one-repeat unit derivatives). MJ networks of 17-STR marker R1b3 Y-chromosome haplotypes, sampled in northwestern (n=166) (B) and southwestern (n=125) (C) Ireland. Each circle represents a different Y-chromosome haplotype, with area proportional to frequency. Line length between haplotypes shows mutational divergence. The IMH (filled red) and one-step neighbors predominate in the northwest, whereas this lineage is virtually absent in the southwest. The synthetic surface map was constructed using the ArcView package (version 3.2) (Environmental Systems Research Institute). Observed frequencies in nine Irish sample groupings of similar size (geographic coordinates marked with a green X) were used, according to the inverse-weighting method, to interpolate the frequency at other coordinates, generating 10 equal-interval surface contours.

Frequency distributions of STR mutational steps from the IMH of all haplotypes in three different groupings. In each case, a minority of non-R1b3 haplotypes was excluded as known outliers. Notably, the sample of subjects with surnames linked by genealogical tradition to the Uí Néill dynasty shows a significantly reduced pattern of divergence from this central haplotype when compared with the background normal distribution seen in the Irish population generally. The powerful legacy of the IMH ancestor on the population structure of the northwestern region is borne out by the disrupted distribution observed in this area. The Uí Néill surname samples were not genotyped for binary markers, since it became apparent during that general population survey that R1b3 chromosomes could be readily detected through STR profiles alone. The Uí Néill sample population was composed of the following surnames (sample number): (O’)Gallagher (12), (O’)Boyle (9), (O’)Doherty (5), O’Donnell (4), O’Connor (3), Cannon (3), Bradley (2), O’Reilly (2), Flynn (2), (Mc)Kee (2), Campbell (1), Devlin (1), Donnelly (1), Egan (1), Gormley (1), Hynes (1), McCaul (1), McGovern (1), McLoughlin (1), McManus (1), McMenamin (1), Molloy (1), O’Kane (1), O’Rourke (1), and Quinn (1).