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RecoverY: K-mer based read classification for Y-chromosome specific sequencing and assembly

By Samarth Rangavittal, Robert S. Harris, Monika Cechova, Marta Tomaszkiewicz, Rayan Chikhi, Kateryna D. Makova, Paul Medvedev

Posted 14 Jun 2017
bioRxiv DOI: 10.1101/148114 (published DOI: 10.1093/bioinformatics/btx771)

Motivation: The haploid mammalian Y chromosome is usually under-represented in genome assemblies due to high repeat content and low depth due to its haploid nature. One strategy to ameliorate the low coverage of Y sequences is to experimentally enrich Y-specific material before assembly. Since the enrichment process is imperfect, algorithms are needed to identify putative Y-specific reads prior to downstream assembly. A strategy that uses k-mer abundances to identify such reads was used to assemble the gorilla Y (Tomaszkiewicz et al 2016). However, the strategy required the manual setting of key parameters, a time-consuming process leading to sub-optimal assemblies. Results: We develop a method, RecoverY, that selects Y-specific reads by automatically choosing the abundance level at which a k-mer is deemed to originate from the Y. This algorithm uses prior knowledge about the Y chromosome of a related species or known Y transcript sequences. We evaluate RecoverY on both simulated and real data, for human and gorilla, and investigate its robustness to important parameters. We show that RecoverY leads to a vastly superior assembly compared to alternate strategies of filtering the reads or contigs. Compared to the preliminary strategy used in Tomaszkiewicz et al (2016), we achieve a 33% improvement in assembly size and a 20% improvement in the NG50, demonstrating the power of automatic parameter selection. Availability: Our tool RecoverY is freely available at https://github.com/makovalab-psu/RecoverY Contact: kmakova@bx.psu.edu, pashadag@cse.psu.edu

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