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Newfoundland and Labrador: A mosaic founder population of an Irish and British diaspora
Newfoundland and Labrador: A mosaic founder population of an Irish and British diaspora from 300 years ago
Next, we investigated if any specific IBD-cluster of Irish or British individuals were driving these English/Irish signals. Considering individual source clusters that contribute substantially to any one NL target cluster (i.e., > 5%), we indeed find specific regional affinity within the English and Irish ancestry components (Figure 4C). The English component is driven by the S&W England cluster, as well as Corn. & Devon. The Irish component is largely driven by clusters with individuals who have recent genealogical ancestry (i.e., from the 1850s) from the Wexford and Waterford regions of southern Ireland, primarily N&W Munster and SE Leinster. Both these English and Irish contributions to Irish-British IBD-segment sharing with NL are strikingly supportive of historical records which show the migrants who migrated to NL can be traced back to communities from these regions in Britain and Ireland2. Moreover, the contributions from each individual Irish/British cluster to the Irish or British ancestry profile in NL are in similar proportions across NL clusters. This is suggestive of a single source of the Irish and British ancestry in NL, i.e., that the Irish or British ancestry in NL is not from multiple waves from different regions in Ireland or Britain.This sharing signal in the southwest of NL of Irish haplotypes from the southeast of Ireland is further supported in an “unsupervised” form of the nnls method where we consider each NL or Irish-British cluster as a mixture of shared IBD from any other NL or Irish-British cluster (Supplemental Data 4.3). This analysis shows that whilst most NL clusters predominantly share IBD-contributions from other NL clusters, reflective of their shared ancestry, some clusters such as Burin E 1 or Avalon Pen. still present substantial ancestry contributions from the N&W Munster and SE Leinster clusters. Furthermore, we tested this mixture of Irish and British haplotypes with the fastGLOBETROTTER algorithm, whose mixture model agrees with an Irish ancestry source best represented by N&W Munster and SE Leinster (see Supplemental Data 5).In an analysis of 1,807 Newfoundland and Labrador individuals we have elucidated the demographic history of European ancestry within NL. Irish and British settlers whose ancestry is shared predominantly with the southeast of Ireland and the southwest of England, respectively, underwent a genetic bottleneck approximately 10 to 15 generations ago (300 to 450 years ago assuming generational time of 30 years). This mixture of south-western English and south-eastern Irish ancestry was distributed unevenly across NL, with Irish ancestry predominant in the south and south-east, and English ancestry predominant elsewhere. Post-migration, genetic structure shows geographic stratification around the bays of the island due to population isolation and then expansion. In these populations genetic homogeneity was elevated with increased haplotype sharing both between and within individuals. The St John’s region of NL in northern Avalon Peninsula is associated with wide-spread haplotype sharing with other regions of NL, suggesting that the urbanarea was a target of post-settlement migration and resultant admixture from across the province.They were limited from exploring French ancestry in NL as there was a lack of substantial French samples. (What's new?)Surprisingly, within our analysis of Britain and Ireland to identify reference clusters for ancestry estimation, we found our IBD-network method was able to detect population structure within England that the fineSTRUCTURE method was unable to20. This allowed us to genetically differentiate the south-west of England from the rest of England and highlights the potential of relatively simple IBD-based clustering methods that not only scale to large datasets but provide novel insights where other more computationally intensive methods cannot. It is possible that the IBD-based and ChromoPainter-based approaches are accessing subtly different time-periods of coalescing genealogies, hence their differing power to detect structure in different regions of Britain. To further highlight this, although IBD-based methods were able to show structure in the south of England, fineSTRUCTURE methods were able to differentiate more clusters in north England than our IBDbased approach20.
https://www.biorxiv.org/content/10.1...593v2.full.pdfIn conclusion, we have performed a systematic analysis of the European ancestry within NL. We have highlighted the role of south-western English and south-eastern Irish settlers in forming a genetic landscape with footprints of a substantial bottleneck forming about 10-15 generations ago, consistent with historical records of substantial migration from Ireland and Britain to NL. This bottleneck, and subsequent isolation and expansion of population around the bays of NL, has shaped a genetic landscape with both high differentiation and haplotype sharing within communities. NL’s demographic history has left a unique genetic background, and preliminary data shows that this includes an elevation of normally rare genetic variation to higher frequencies. Coupled with high homogeneity, this genetic profile is ideal for a large population-based genetic mapping efforts, like those achieved in Iceland41, Finland15, and the Orcadian38 populations. Our results not only highlight the use of annotated population genetic references in elucidating human history but also characterise the genetic profile population ideal for human genetic disease mapping in unprecedented detail.
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Originally Posted by Grace O'Malley
Canada
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