engleski

An Evolutionary Analysis of Orphan Genes in Drosophila

Orphan genes are protein coding regions that have no recognizable homologue in distantly related species. A substantial fraction of coding regions in any genome sequenced consists of such orphan genes, but the evolutionary and functional significance of orphan genes is not understood. We present a re-analysis of the Drosophila melanogaster proteome that shows that there are still between 26 - 29% of all proteins without a significant match with noninsect sequences and that these orphans are under-represented in genetic screens. To analyze the characteristics of orphan genes in Drosophila, we used sequence comparisons between cDNAs retrieved from two D. yakuba libraries and their corresponding D. melanogaster anthologies. We find that a cDNA library from adults yields twice as many orphan genes as such a library from embryos. The orphan genes evolve on average more than three times faster than nonorphan genes, although the width of the evolutionary rate distribution is similar for the two classes. In particular, some orphan genes show very low substitution rates that are comparable to otherwise highly conserved genes. We propose a model suggesting that orphans may be involved in the evolution of adaptive traits, and that slow-evolving orphan genes may be particularly interesting candidate genes for identifying lineage-specific adaptations.

orphan genes; evolution; Drosophila; genome

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