Much Ado About Orthologs Consequences of Duplication and Speciation in Gene Evolution

Meeting Abstract

18-4  Friday, Jan. 4 10:45 – 11:00  Much Ado About Orthologs: Consequences of Duplication and Speciation in Gene Evolution DAVID, KT*; OAKS, JR; HALANYCH, KM; Auburn University; Auburn University; Auburn University

In eukaryotic lineages, genes typically replicate through either speciation or gene duplication events. After a speciation event, resulting gene copies (orthologs) are generally expected to maintain similar evolutionary rates, as function is typically conserved. After a duplication event, however, resulting gene copies (paralogs) may differ in evolutionary rates and a broader set of possible fates may be realized, including partial (subfunctionalization) or complete loss of function (nonfunctionalization), as well as gain of new function (neofunctionalization) in at least one of the descendant copies. Many popular gene annotation databases indirectly assume conservation of substitution rates between orthologs and divergence of rates between paralogs. Unfortunately, studies which explicitly compare evolutionary processes between speciation and duplication events are rare and conflicting. To provide an empirical framework of ortholog/paralog evolution, we estimated the rate ratio of nonsynonymous to synonymous substitutions (dN/dS) of 213,808 branches in 8,470 gene trees across 77 vertebrate taxa. Overall, we found lineages descended from speciation events had significantly (p<0.001) more similar dN/dS ratios to one another than did lineages descended from duplication events. However, there are several branches near the base of the vertebrate tree where we either do not recover significant differences between change in dN/dS between orthologous and paralogous branches or find significant support for the opposite hypothesis: more similar dN/dS ratios between paralogous branches than orthologous branches. We discuss possible interpretations of this surprising result and conclude that orthologous relationships are often, but not always, associated with more conserved evolutionary rates than paralogous relationships.

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