As the zebra finch genome sequence is not yet available we do not have any direct evidence that the 176 genes from the Z chromosome of chicken are also sex-linked in zebra finch. However, there is strong indirect support of synteny for the chicken and zebra finch Z chromosomes from a number of sources. Chromosome-specific painting probes from the chicken Z chromosome only hybridize to the Z chromosome in zebra finch metaphase spreads (Itoh and Arnold 2005). The same pattern is consistently seen for birds representing several divergent avian lineages (Griffin et al. 2007), including the most basal clade of ratites (Shetty et al. 1999), suggesting that the Z chromosome has not been involved in any major inter-chromosomal rearrangements during avian evolution. Moreover, at the level of individual genes, Itoh et al. (2006), using in situ hybridization, found 14 out of 14 genes Z-linked in chicken to map to the Z chromosome of zebra finch. Similarly, Backström et al. (2006), using linkage analysis, found 23 out of 23 evenly distributed genes from the chicken Z chromosome to map to the Z chromosome of the collared flycatcher (Ficedula hypoleuca), another song bird species of the same order as zebra finch (Passeriformes).
Cytogenetic data indicate that chicken and zebra finch chromosomes 1-10 are largely syntenic. One exception is chromosome 4p in chicken, which was added to the ancestral chromosome 4 by fusion with a microchromosome in the galliform lineage, subsequent to the split of chicken and turkey (ICGSC 2004). Genes from this small chromosomal segment were therefore excluded from the analysis of substitution rates (n=121), as well as for the those of genetic diversity (BBSRC, n=21; ICPMC, n=219) in chromosomes 1-10.
Backström, N., Brandström, M., Gustafsson, L., Qvarnström, A., Cheng, H., and
Ellegren, H. 2006. Genetic mapping in a natural population of collared flycatchers (Ficedula albicollis): Conserved synteny but gene order
rearrangements on the avian Z chromosome. Genetics 174: 377-386
Griffin, D.K., Robertson, L.B.W., Tempest, H.G., and Skinner, B.M. 2007. The evolution of the avian genome as revealed by comparative molecular cytogenetics. Cytogen. Gen. Res., in press.
International Chicken Genome Sequencing Consortium. 2004. Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution. Nature 432: 695-716.
Itoh, Y., Kampf, K, and Arnold, A.P. 2006. Assignment of human X-linked genes to a zebra finch microchromosome by in situ hybridization of BAC clones. Cytogen. Gen. Res. 112: 342M-U20
Itoh, Y., and Arnold, A.P. 2005. Chromosomal polymorphism and comparative painting analysis in the zebra finch. Chrom. Res. 13: 47-56
Shetty, S., Griffin, D.K., and Graves, J.A.M. 1999. Comparative painting reveals strong chromosome homology over 80 million years of bird evolution. Chrom. Res. 7: 289-295