The goal of this study is to compare the mouse strains C57BL/6 and CAST/EiJ and their hybrids of forward and reverse mating (F1i and F1r respectively) in behavioral, molecular and electrophysiological level. We examine the effects of parental genotypes on the offspring phenotypes using behavioral studies, electrophysiology and RNA-seq. We show that despite having the same genome, the F1i and the F1r hybrids display different phenotypes, and this may be due to having opposite parental sources of the same genome. Overall design: Whole brain mRNA profiles of B6, CAST, B6 x CAST (F1i) and CAST x B6 (F1r) mice