Author information: Birds show female heterogamety, divine brown porno ZZ males and ZW females.
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It is still not clear whether the Sex 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 modeal 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. Here Sex 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 upskirtteens 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.
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Reports of modeal aneuploids and triploids are also consistent with this hypothesis. Copyright S. Karger AG, Basel.