It remains a key challenge in evolutionary biology to learn how variation in genotype within populations of organisms is ultimately associated with adaptive variation in phenotype. Several new molecular and genomic approaches offer promising opportunities to meet this challenge. Among these are DNA microarrays and RNA-seq, which enable expression profiling (genome-wide analysis of the relative abundances of gene transcripts). In principle, these approaches can form a bridge connecting genotype with phenotype, because specific, reproducible patterns of transcription associated with particular genotypes may also be associated with particular phenotypes and affect fitness. Application of expression profiling to natural populations to study the evolution of whole genomes is still in its earliest stages. In our laboratory, we have focused our genomic efforts on the model organisms, yeast and Drosophila.
Previously we provided evidence that sexual selection and sexual differentiation are important in driving the evolution of gene expression networks. For example, among genes that have evolved differences in expression between two Drosophila species that diverged 2.5 million years ago, more than 80% of the differences occur either in one sex only or else involve the gain, loss or reversal of sex-biased expression.
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