Strong evolutionary convergence of receptor-binding protein spike between COVID-19 and SARS-related coronaviruses

Yonghua Wu

We analyzed relative selection intensity using the RELAX 19 program, available from the Datamonkey webserver (http://test.datamonkey.org/relax). RELAX is a hypothesis testing framework, and it can be used to test whether selection strength has been relaxed or intensified along a certain branch or lineage. For analyses, RELAX calculates a selection intensity parameter value (k), and k > 1 shows an intensified selection, while k < 1 indicates a relaxed selection, assuming a priori partitioning of the test branches and reference branches. We would expect that an intensified selection shows ω categories away from neutrality (ω = 1), while a relaxed selection is expected to show ω categories converging to neutrality (ω = 1). Statistical significance was evaluated by LRT by comparing an alternative model with . CC-BY-NC-ND 4.0 International license author/funder. It is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.04.975995 doi: bioRxiv preprint a null model. The null model assumes k = 1 and the same ω distribution for both test and reference branches, while the alternative model assumes that k is a free parameter, and the test and reference branches may have different ω distributions.