Canary-specific estrogen response elements (see inserts) occur in the orthologous promoters of canary and zebra finch genes. (A) Genes with orthologous promoters but that contain nucleotide sequences in zebra finch deviating from known ERE sequences (see insert in (A)). (B) Genes with EREs in the promoters of canaries for which we did not find orthologous promoters in zebra finch. In these cases, sequence analysis of 1 kb of the putative promoter region of the zebra finch did not identify EREs. The 15 genes analysed in detail were randomly selected from the list of genes with canary-specific EREs. Thus, of the about 550 seasonally up-regulated genes that contain canary-specific EREs, about one-half are classified as type ‘A’ and the other half as type ‘B’. Some genes such as SRGAP3 are in both categories. Orthologous promoters are in yellow, those containing EREs are in orange, and heterologous promoters are in red.