Schematic diagram of the frequency distribution of the sb c<i>yp19a</i> promoter methylation levels in females and males.

<p>Low methylation levels (purple curve) of the sb <i>cyp19a</i> promoter are typical of females and are required for ovarian differentiation. Males typically show high methylation levels (blue curve) of the <i>cyp19a</i> 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 <i>cyp19a</i> 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.</p>