Schematic diagram of the frequency distribution of the sb cyp19a promoter methylation levels in females and males.

Low methylation levels (purple curve) of the sb cyp19a promoter are typical of females and are required for ovarian differentiation. Males typically show high methylation levels (blue curve) of the cyp19a promoter. This blocks aromatase transcription and induces testicular differentiation caused by lack of estrogens. As shown in this study, high temperatures (HT) during the thermosensitive period increase methylation levels of the sb cyp19a promoter (red curve), shifting the female distribution closer to that of males. The dashed area represents the fraction of genotypic females that are sex reversed into phenotypic males by high temperature.