qPCR analysis of male-specific genes. qPCR analysis of relative RNA levels in male (M) and female (F) livers at 3, 4 and 8 wk, as marked at the bottom. Data shown for the four indicated adult male-specific genes are normalized to the 18S RNA of each sample, and based on n = 9-10 individuals per group (mean ± SEM). Statistical analysis (two-way ANOVA with Bonferroni post tests) was as follows: * p < 0.01, and ** p < 0.001, for male vs. female comparisons at each age; + p < 0.05, ++ p < 0.01, and +++ p < 0.001, for 4 wk vs. 3 wk, and for 8 wk vs. 4 wk comparisons within each sex. Very similar results were obtained by microarray analysis (Additional file 8).