Fig. 2.

Comparison of the male:female (M:F) expression ratio in brain for orthologous Z-chromosome genes in ostrich and chicken. (A) Genes from clusters on the ostrich Z-chromosome with an equal male:female expression ratio, and (B) genes from clusters on the ostrich Z-chromosome with a 2-fold excess of male expression. Chicken data are without replicates, likely explaining the larger variation among genes for this species.