Comparison of male and female gene expression in birds. The bar graphs compare the percentages of Z (yellow) and A (blue) genes that are expressed at significantly higher levels in males vs females (M > F) or are expressed equally or more highly in females (M ≤ F). Four tissues are shown for zebra finch (a) and three for chick embryo (b). In all tissues, a significantly greater proportion of Z-linked genes, relative to A genes, were expressed at higher levels in males than females.
Itoh et al. Journal of Biology 2007 6:2 doi:10.1186/jbiol53