Fig. 4.
—Analyses of XY gametologues. (a) Boxplots representing the current/ancestral expression ratio of X gametologues in females, X gametologues in males, Y gametologues in males, and the added expression of X and Y gametologues in males (n = 10 genes). Significant differences (Mann–Whitney U test). Genes with the highest and lowest expression ratios are indicated. (b) Boxplots representing the expression balance of XY gametologues between the two sexes, that is, the X gametologues expression levels in males compared with those in females, as well as the added expression levels of X and Y gametologues in males compared with the expression levels of the X gametologues in females (n = 10 genes). Genes with the highest and lowest expression ratios are indicated. (c) Tissue-specificity index (TSI) of XY gametologues and proto-sex genes (tissue-specificity of orthologous genes in the chicken and the green anole) in males and females. Genes with a tissue-specificity index below 0.7 are colored in gray. Genes with a tissue-specificity index above 0.7 are filled using the colors shown at the bottom of the figure; TSI values are indicated. (d) dS tree built using the concatenated coding nucleotide sequences of stratum 1 genes and orthologous sequences in other tetrapod species. The age of the sex chromosome system in corytophanids was obtained by comparing specific branch lengths and the age at specific nodes (see Materials and Methods). Age estimates for specific nodes are based on Zheng and Wiens (2016). Millions of years ago are denoted by “Ma.”