Gene Duplication and the Genome Distribution of Sex-Biased Genes

Figure 2

Sex-biased expression can be acquired in three different ways. (1) Changes in the cis-regulatory regions or in trans-acting factors can lead to a gene that is more highly expressed in females (pink) than in males or more highly expressed in males (blue) than in females. (2) A gene can have alternative transcripts through alternative splicing. One of those transcripts might be sex-biased in expression. This sex-biased expression can often, though not always, be detected by standard methods (e.g., microarray analyses) if it leads to higher expression in one sex, but it may require direct analysis of alternative transcripts. (3) Gene duplication can lead to the creation of sex-biased genes (e.g., a male-biased gene) through RNA- or DNA-mediated gene duplication. Gene duplication might create one or two sex-biased genes. For details of the proposed models, see Table 1. In the three instances, the exons might specialize. Gene expression patterns are shown with filled boxes and exons with open boxes. Green and orange refer to expression in both sexes. Pink refers to female-specific expression or specialization of an exon. Blue refers to male-specific expression or specialization of an exon.