title: Deficit of mitonuclear genes on the human X chromosome predates sex chromosome formation.
abstract: Two taxa studied to date, the therian mammals and Caenorhabditis elegans, display underrepresentations of mitonuclear genes (mt-N genes, nuclear genes whose products are imported to and act within the mitochondria) on their X chromosomes. This pattern has been interpreted as the result of sexual conflict driving mt-N genes off of the X chromosome. However, studies in several other species have failed to detect a convergent biased distribution of sex-linked mt-N genes, leading to questions over the generality of the role of sexual conflict in shaping the distribution of mt-N genes. Here we tested whether mt-N genes moved off of the therian X chromosome following sex chromosome formation, consistent with the role of sexual conflict, or whether the paucity of mt-N genes on the therian X is a chance result of an underrepresentation on the ancestral regions that formed the X chromosome. We used a synteny-based approach to identify the ancestral regions in the platypus and chicken genomes that later formed the therian X chromosome. We then quantified the movement of mt-N genes on and off of the X chromosome and the distribution of mt-N genes on the human X and ancestral X regions. We failed to find an excess of mt-N gene movement off of the X. The bias of mt-N genes on ancestral therian X chromosomes was also not significantly different from the biases on the human X. Together our results suggest that, rather than conflict driving mt-N genes off of the mammalian X, random biases on chromosomes that formed the X chromosome could explain the paucity of mt-N genes in the therian lineage.
authors: Department of Genetics, Evolution and Environment, University College London, United Kingdom r.dean@ucl.ac.uk.
authors: Rebecca
authors: R
authors: Dean
authors: Department of Genetics, Evolution and Environment, University College London, United Kingdom.
authors: Fabian
authors: F
authors: Zimmer
authors: Department of Genetics, Evolution and Environment, University College London, United Kingdom.
authors: Judith E
authors: JE
authors: Mank
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000235:genetics*; D002645:Chickens / Q000235:genetics; D041321:Chromosomes, Human, X / Q000235:genetics*; D050259:Genes, Mitochondrial / Q000235:genetics*; D006801:Humans; D058977:Molecular Sequence Annotation; D010987:Platypus / Q000235:genetics; D026801:Synteny / Q000235:genetics
keywords: mitochondria; sex chromosomes; sexual conflict; synteny
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