The contributions of sex, genotype and age to transcriptional variance in Drosophila melanogaster

Here we present a statistically rigorous approach to quantifying microarray expression data that allows the relative effects of multiple classes of tr eatment to be compared and incorporates analytical methods that are common to quantitative genetics. From the magnitude of gene effects and contributi ons of variance components, we find that gene expression in adult flies is affected most strongly by sex, less so by genotype and only weakly by age ( for 1- and 6-wk flies); in addition, sex x genotype interactions may be pre sent for as much as 10% of the Drosophila transcriptome. This interpretatio n is compromised to some extent by statistical issues relating to power and experimental design. Nevertheless, we show that changes in expression as s mall as 1.2-fold can be highly significant. Genotypic contributions to tran scriptional variance may be of a similar magnitude to those relating to som e quantitative phenotypes and should be considered when assessing the signi ficance of experimental treatments.