Comparison of the chicken and zebra finch Z chromosomes shows evolutionary rearrangements

Using fluorescent in-situ hybridization (FISH) of zebra finch (Taeniopygia guttata) bacterial artificial chromosome (BAC) clones, we determined the chromosomal localizations of 14 zebra finch genes that are Z-linked in chickens: ATP5A1, CHD1, NR2F1, DMRT1, PAM, GHR, HSD17B4, NIPBL, ACO1, HINT1, SMAD2, SPIN, NTRK2 and UBE2R2. All 14 genes also map to the zebra finch Z chromosome, indicating substantial conservation of gene content on the Z chromosome in the two avian lineages. However, the physical order of these genes on the zebra finch Z chromosome differed from that of the chicken, in a pattern that would have required several inversions since the two lineages diverged. Eight of 14 zebra finch BAC DNA showed cross-hybridization to the W chromosome, usually to the entire W chromosome, suggesting that repetitive sequences are shared by the W and Z chromosomes. These repetitive sequences likely evolved in the finch lineage after it diverged from the Galliform lineage.