Spermatogenesis occurs in successive mitotic, meiotic and post–meiotic phases and genes expressed during this process encode proteins necessary for processes specific to the different phases of germ cell development. Some genes encode proteins with essential roles in structures or functions specific to spermatogenic cells, are expressed in developmentally regulated patterns and are transcribed only in, or produce mRNAs unique to, spermatogenic cells. They are referred to as chauvinist genes, because male germ cells favor their expression with such strong prejudice. The expression of these genes is influenced by extrinsic cues, but is determined primarily by the intrinsic genetic program of spermatogenic cells. These processes are subject to transcriptional, translational and post–translational regulation. However, many aspects of the mechanisms regulating gene expression in spermatogenic cells remain to be determined.