The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is used for sex-determining as the presence of the Y chromosome typically causes offspring produced in sexual reproduction to develop phenotypically male. In mammals, the Y chromosome contains the SRY gene, which usually triggers the differentiation of male gonads. The Y chromosome is typically only passed from male parents to male offspring.