Histogram showing the observed and expected genomic distribution of sex-biased genes. The number of sex-biased genes for each chromosomal category in (a) zebra finch and (b) common whitethroat. Annotations achieved by BLASTs of the EST sequences on the array against the zebra finch sequence assembly (build 3.2.4). Significant hits have a hit of E = 10-20 or lower, and "no annotation" indicates that the EST sequence has either a significant hit against TguUnknown or no significant hit against any of the zebra finch chromosomes. Numbers above bars represent number of genes in each category.