Accurate prediction of orthologs in the presence of divergence after duplication

Abstract

Motivation: When gene duplication occurs, one of the copies may become free of selective pressure and evolve at an accelerated pace. This has important consequences on the prediction of orthology relationships, since two orthologous genes separated by divergence after duplication may differ in both sequence and function. In this work, we make the distinction between the primary orthologs, which have not been affected by accelerated mutation rates on their evolutionary path, and the secondary orthologs, which have. Similarity-based prediction methods will tend to miss secondary orthologs, whereas phylogenybased methods cannot separate primary and secondary orthologs. However, both types of orthology have applications in important areas such as gene function prediction and phylogenetic reconstruction, motivating the need for methods that can distinguish the two types. Results: We formalize the notion of divergence after duplication, and provide a theoretical basis for the inference of primary and secondary orthologs. We then put these ideas to practice with the HyPPO (Hybrid Prediction of Paralogs and Orthologs) framework, which combines ideas from both similarity and phylogeny approaches. We apply our method to simulated and empirical datasets, and show that we achieve superior accuracy in predicting primary orthologs, secondary orthologs and paralogs. Availability: HyPPO is a modular framework with a core developed in Python, and is provided with a variety of C++ modules. The source code is available at https://github.com/manuellafond/HyPPO.

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“…The PIC was more powerful than the pairwise approach under this model (S1 Table). Thirdly and most worryingly, when both sequence and trait Lafond et al 2018). Thus the scenario of these simulations is expected to be widespread in real data.…”