From Fertilization to Adult Sexual Behavior In our section on molecular epigenetics from 1996 we wrote: Genomic-imprinting is also manifest in specific parts of the X-inactivation region’s related XIST gene. Here male- and female-specific methyl-group patterns participate in X-inactivation in females and also in the preferential inactivation of the paternal X in human placentae of female concepti (Harrison, 1989; Monk, 1995). This process indicates that tissues of the early conceptus can sense and react differentially to epigenetic sexual dimorphisms on…