Hens, cocks and avian sex determination. A quest for genes on Z or W?
The sex of an individual is generally determined genetically by genes on one of the two sex chromosomes. In mammals, for instance, the presence of the male-specific Y chromosome confers maleness, whereas in Drosophila melanogaster and CAENORHABDITIS: elegans it is the number of X chromosomes that matters. For birds (males ZZ, females ZW), however, the situation remains unclear. The recent discovery that the Z-linked DMRT1 gene, which is conserved across phyla as a gene involved in sexual differentiation, is expressed early in male development suggests that it might be the number of Z chromosomes that regulate sex in birds. On the other hand, the recent identification of the first protein unique to female birds, encoded by the W-linked PKCIW gene, and the observation that it is expressed early in female gonads, suggests that the W chromosome plays a role in avian sexual differentiation. Clearly defining the roles of the DMRT1 and PKC1W genes in gonadal development, and ultimately determining whether avian sex is dependent on Z or W, will require transgenic experiments.
Ellegren
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Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden. Hans.Ellegren@ebc.uu.se
D000818:Animals; D001717:Birds / Q000235:genetics*; D005260:Female; D018628:Gene Dosage; D008297:Male; D008957:Models, Genetic; D009419:Nerve Tissue Proteins / Q000235:genetics; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes; D014157:Transcription Factors / Q000235:genetics
C110547:DMRT1 protein; D009419:Nerve Tissue Proteins; D014157:Transcription Factors; D011493:Protein Kinase C