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I'm presently reading this and will add as I go along. The paper can be retrieved from here. By Dr Lara Cassidy.
http://www.tara.tcd.ie/handle/2262/82960
Neolithic individuals were found to place overwhelmingly within haplogroup I2a (Electronic Data TableS5-7), one of the dominant lineages of the European Mesolithic and commonly observed in other western Neolithic populations (Haak et al. 2015; Mathieson et al. 2015; Olalde et al. 2017). As expected, Mesolithic samples show more basal lineages with respect to the Neolithic cohort, a significant number of whom placed within the subclade I2a2a1-M284, found almost exclusively in Britain today.Irish mesolithic samples are indistinguishable from other European HGs.A near complete turnover is then witnessed in the Chalcolithic and Early Bronze Age, with virtually all samples from this time onwards belonging to the R1b-L151 haplogroup, associated with the Atlantic Modal Haplotype. This lineage forms a downstream branch of R1b-M269, the most prevalent haplogroup in western Europe today (Myres et al. 2011). It was possible to place a further majority of samples (81.8%) into the subclade R1b-L21, a haplogroup whose distribution shows a steep and somewhat restricted peak in modern Ireland, where it accounts for almost half of male lineages (Myres et al. 2011). Only one Y chromosome examined fell outside R1b-M269 after the Neolithic period, belonging to an Early Bronze Age individual from the southwest, Killuragh1, who placed within I2a2a1-M284.
However, a notable exception is the Palaeolithic sample from El Miron in Spain, belonging to the Magdalenian culture, who, within a majority “red” background, possesses a mosaic of components that dominate in diverse modern populations, such as Papuans, East Asians and Indians. This noisy signal is likely to represent deep pre-glacial population structure between Iberian refugia populations and those further east in Italy and the Balkans (Fu et al. 2016). The signature is also seen to a lesser extent in the earliest Mesolithic sample of the region, but disappears in later Spanish samples. Importantly, Irish Mesolithic individuals do not show any detectable level of this ancestry, displaying profiles more similar to Palaeolithic samples from Switzerland and Italy.
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