Mammalian males and females have many phenotypic differences. These differences, collectively referred to as sexual dimorphism, are the consequence of natural and sexual selection for phenotypic traits that affect the fitness of each sex and are encoded in the genome. Part of the underlying genomic differences between the sexes are found on sex specific (the Y) or sex biased chromosomes (the X), while many sexually dimorphic traits probably result from autosomal gene expression differences in sex specific or somatic tissues. However, the origin and evolution of sex-biased genes in mammals has not been studied in detail. I propose to generate the first detailed qualitative and quantitative transcriptome data using next generation sequencing technologies for a unique collection of germline and somatic tissues from representatives of all major mammalian lineages: placental mammals, marsupials, and the egg-laying monotremes. Together with detailed transcriptome data from birds (the evolutionary sister lineage), complementary experiments (e.g. methylome analyses), and available genomic resources from these species, these unprecedented data will allow an integrated analysis of the origin and functional evolution of mammalian sex chromosomes, the emergence of new sex biased genes, and the evolution of gene expression in germline versus somatic tissues in mammals at large. The proposed work will thus substantially increase our power to understand how mammalian genomes evolved the capacity to produce such pronounced sexually dimorphic traits. Beyond research pertaining to sex biased genome evolution, our data will represent a unique resource for future investigations of mammalian gene functions and serve as a basis for exploring the evolution of other mammal specific phenotypes.
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