Sex and death in birds: A model of dosage compensation that predicts lethality of sex chromosome aneuploidsGraves J.A.M.
Research School of Biological Sciences, The Australian National University, Canberra (Australia)
Birds show female heterogamety, with ZZ males and ZW females. It is still not clear whether the W is female-determining, or whether two doses of the Z chromosomes are male-determining, or both. This question could easily be settled by the sexual phenotypes of ZZW and ZO birds, in the same way that the sexual phenotypes of XXY and XO showed that the Y is male determining in humans, but that the dosage of an X-borne gene determines sex in Drosophila. However, despite extensive searches, no ZZW or ZO diploid birds have been satisfactorily documented, so we must assume that these genotypes are embryonic lethals. Given that ZW and ZZ are viable and the W contains few genes it is not clear why this should be so. Here I propose that sex chromosome aneuploids are lethal in chicken because, to achieve dosage compensation, a locus on the W chromosome controls the upregulation of genes on the Z in ZW females. ZO birds would therefore have only half the normal dose of Z-linked gene product and ZZW would have twice the amount, both of which would undoubtedly be incompatible with life. Reports of other aneuploids and triploids are also consistent with this hypothesis.
© 2003 S. Karger AG, Basel
Request reprints from Professor Jennifer A. Marshall Graves
Research School of Biological Sciences
The Australian National University, Canberra, ACT 2601 (Australia)
telephone: 61-2-6125-2492; fax: 61-2-6125-4891
Manuscript received 30 May 2003;
revision accepted 27 August 2003.
Number of Print Pages : 5
Number of Figures : 1, Number of Tables : 2, Number of References : 33
Cytogenetic and Genome Research
Formerly ‘Cytogenetics and Cell Genetics’
Vol. 101, No. 3-4, Year 2003 (Cover Date: 2003)
Journal Editor: H.P. Klinger, Bronx, N.Y.; M. Schmid, Würzburg
ISSN: 1424–8581 (print), 1424–859X (Online)
For additional information: http://www.karger.com/journals/cgr