X-ing Out Male Expression?

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Science  31 Jan 2003:
Vol. 299, Issue 5607, pp. 621h
DOI: 10.1126/science.299.5607.621h

There is considerable interest in the origin and selection in the sex chromosomes of animals. Because males display one X, one might expect greater selection that is to the male advantage. However, two-thirds of the × chromosomes in a population are contained in females, raising the opposite possibility. Parisi et al. (p. 697, see the Perspective by Schlötterer) now examine global gene expression in the fruit fly, Drosophila, to determine how genes with sex-differential gene expression profiles are distributed among the chromosomes. This analysis shows that more than 30% of the genome is differentially expressed between males and females and most of the sex-biased expression is found in the gonads. In Drosophila males, fewer X-linked genes are expressed in a sex-biased manner, and the few X-linked genes that show male-biased expression are generally not conserved with the mosquito genome. These results suggest that the × chromosome has experienced a “net demasculinization” effect.

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