Environmental factors contribute to the risk for autism spectrum disorders (ASD), and a greater understanding of these factors is needed. Adverse prenatal conditions can affect the development of the infant brain, increasing the risk for neurobehavioral disabilities, such as autism spectrum disorders (ASD) or anxiety. In total, small-for-gestational age (SGA) or large-for-gestational age (LGA) may affect over half a million American infants every year, and epidemiological evidence indicates that both SGA and LGA infants are at an increased risk for ASD. Researchers have developed two mouse models based on an adverse in utero environment that result in SGA or LGA offspring by feeding pregnant dams a low protein diet or high fat diet, respectively. Expression levels of the Rett Syndrome gene, MeCP2, are significantly different in both SGA and LGA offspring, identifying MeCP2 expression as a potential important epigenetic mechanism responsive to adverse in utero conditions. In this study, researchers will use these animal models to examine brain and behavior changes in response to adverse in utero conditions. Specifically, researchers will examine: 1) social and anxiety-related behaviors in SGA and LGA offspring and 2) genome-wide gene expression changes in SGA and LGA mice. The development of these models will allow for future studies of neurobiological mechanisms that link adverse in utero environment and altered social and emotional behaviors with an eventual goal of the development of targeted therapeutics and interventions.