Given the large sex differences in the prevalence of several neurobehavioral diseases (for example, autism is found 4 times more often in boys than in girls), this study focuses on epigenetic modification of mechanisms that underlie sex differences in behavior. This study will evaluate whether the endocrine disrupting compound, bisphenol A (BPA), can modify sex differences in behavior and, if so, whether it acts on X-chromosome genes that may be linked to diseases. Genetically engineered mice, molecular, genetic ,and behavioral methods will be used to reveal epigenetic interactions between sex chromosome genes and BPA. Specifically, the effects of sex chromosomes and BPA on juvenile social behavior in mice will be assessed, and gene expression arrays of candidate genes affected by BPA exposure during neural development will be conducted. The effects of BPA on DNA methylation and histone modification will also be examined. The goal of this research is to find genes and processes that can help diagnose, treat, and prevent mental illnesses.