The worm Caenorhabditis elegans is a hermaphroditic organism when genotypically XX. Male animals, which do not produce oocytes and which have masculinized morphology, are genetically X0, i.e., they have only one copy of the X chromosome. Two different pathways of sexual determination with several common components control somatic cell sexual characteristics and germ-cell sexual characteristics. One component common to both tissues is the TRA-2 gene, which expresses two proteins. One of these is TRA-2A, a membrane protein, which can be cleaved to release the intracelluar domain (TRA-2Aic), which, in oocytes, can also be directly transcribed from the TRA-2 gene. Wang and Kimble identified a physical interaction between TRA-2ic and TRA-1, a transcription factor that promotes feminization in somatic tissues and masculinization in germ cells. This unexpected physical interaction may provide a mechanism for regulating the different tissue responses that rely on the same components. The importance of this interaction in the specification of germ-cell sexual fate and the lack of a role for this interaction in somatic-cell sexual fate was demonstrated by using genetic interactions in C. elegans.