Transcription factor that plays a key role in male sex determination. Acts both as a transcription repressor and repressor. Expressed in the genital ridge and Wolffian duct prior to sexual differentiation and is expressed at higher levels in ZZ than in ZW embryos. Expressed at stage 19 before sexual differentiation, at stage 25 when the genital ridges are forming and also at stage 31 when sexual differentiation is beginning. Also expressed from stage 25 in the Wolffian ducts. More abundant in ZZ (male) than ZW (female) gonads. Knockdown of DMRT1 in early embryos results in the feminization of male gonads, affecting tissue organization, gene expression and germ cell distribution. These experiments are in support of the Z dosage hypothesis for avian sex determination or at least, for gonadal sex development: according to this theory ZZ males would have a higher dosage of DMRT1 which would initiate testicular differentiation and expression of the key conserved Sertoli cell differentiation factor, SOX9 (PubMed:19710650). Belongs to the DMRT family.