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bioRxiv · 10.1101/028282

Fast and accurate long-range phasing in a UK Biobank cohort

Po-Ru Loh·Pier Francesco Palamara·Alkes L Price
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Abstract

Recent work has leveraged the extensive genotyping of the Icelandic population to perform long-range phasing (LRP), enabling accurate imputation and association analysis of rare variants in target samples typed on genotyping arrays. Here, we develop a fast and accurate LRP method, Eagle, that extends this paradigm to populations with much smaller proportions of genotyped samples by harnessing long (>4cM) identical-by-descent (IBD) tracts shared among distantly related individuals. We applied Eagle to N=150K samples (0.2% of the British population) from the UK Biobank, and we determined that it is 1-2 orders of magnitude faster than existing methods while achieving similar or better phasing accuracy (switch error rate {approx}0.3%, corresponding to perfect phase in most 10Mb segments). We also observed that when used within an imputation pipeline, Eagle pre-phasing improved downstream imputation accuracy compared to pre-phasing in batches using existing methods (as necessary to achieve comparable computational cost).

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Po-Ru Loh, Pier Francesco Palamara, Alkes L Price. 2015-10-04. Fast and accurate long-range phasing in a UK Biobank cohort. https://doi.org/10.1101/028282

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