Estimating the Relative Contributions of New Genes from Retrotransposition and Segmental Duplication Events during Mammalian Evolution

Abstract

Gene duplication has long been recognized as a major force in genome evolution and has recently been recognized as an important source of individual variation. For many years the origin of functional gene duplicates was assumed to be whole or partial genome duplication events, but recently retrotransposition has also been shown to contribute new functional protein coding genes and siRNA's. Here we present a method for the identification and classification of retrotransposed and segmentally duplicated genes and pseudogenes based on local synteny. Using the results of this approach we compare the rates of segmental duplication and retrotransposition in five mammalian genomes and estimate the rate of new functional protein coding gene formation by each mechanism. We find that retrotransposition occurs at a much higher and temporally more variable rate than segmental duplication, and gives rise to many more duplicated sequences over time. While the chance that retrotransposed copies become functional is much lower than that of their segmentally duplicated counterparts, the higher rate of retrotransposition events leads to nearly equal contributions of new genes by each mechanism.