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Dosage compensation is less effective in birds than in mammals.

  • Author(s): Itoh, Yuichiro
  • Melamed, Esther
  • Yang, Xia
  • Kampf, Kathy
  • Wang, Susanna
  • Yehya, Nadir
  • Van Nas, Atila
  • Replogle, Kirstin
  • Band, Mark R
  • Clayton, David F
  • Schadt, Eric E
  • Lusis, Aldons J
  • Arnold, Arthur P
  • et al.

Published Web Location

https://doi.org/10.1186/jbiol53
Abstract

Background

In animals with heteromorphic sex chromosomes, dosage compensation of sex-chromosome genes is thought to be critical for species survival. Diverse molecular mechanisms have evolved to effectively balance the expressed dose of X-linked genes between XX and XY animals, and to balance expression of X and autosomal genes. Dosage compensation is not understood in birds, in which females (ZW) and males (ZZ) differ in the number of Z chromosomes.

Results

Using microarray analysis, we compared the male:female ratio of expression of sets of Z-linked and autosomal genes in two bird species, zebra finch and chicken, and in two mammalian species, mouse and human. Male:female ratios of expression were significantly higher for Z genes than for autosomal genes in several finch and chicken tissues. In contrast, in mouse and human the male:female ratio of expression of X-linked genes is quite similar to that of autosomal genes, indicating effective dosage compensation even in humans, in which a significant percentage of genes escape X-inactivation.

Conclusion

Birds represent an unprecedented case in which genes on one sex chromosome are expressed on average at constitutively higher levels in one sex compared with the other. Sex-chromosome dosage compensation is surprisingly ineffective in birds, suggesting that some genomes can do without effective sex-specific sex-chromosome dosage compensation mechanisms.

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