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, 2 (3), 192-6

Hens, Cocks and Avian Sex Determination. A Quest for Genes on Z or W?


Hens, Cocks and Avian Sex Determination. A Quest for Genes on Z or W?

H Ellegren. EMBO Rep.


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.


Fig. 1. Two potential mechanisms for chromosomal sex determination among birds. (A) the presence of the W chromosome triggers femaleness or (B) the presence of two Z chromosomes confers maleness.
Fig. 2. Transgenic strategies for revealing the mechanism of sex determination among birds. (A) a ZZW bird, (B) a Z0 bird.
Hans Ellegren

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