Number of sex-biased genes per age group. The number of unique, differentially expressed genes exhibiting sex-difference in expression (pairwise t test, FDR 5%, and 1.5 relative fold change between sexes) was calculated for each age group. The total number of sex-biased genes (A) is divided into female- and male-biased genes per age group. 114 sex-biased genes common to 8-, 15-, and 21-week animals (B) were plotted together in order to compare this list of robust sex differences accross all ages. Green, red, and blue lines represent numbers of total, female-biased, and male-biased genes, respectively, at each age group.