Evolutionary stasis: the stable chromosomes of birds.

Evolution at the molecular level is manifested in a variety of types of change in DNA sequences, including changes in the structure and organisation of chromosomes. However, in birds chromosomal evolution occurs at an unusually slow rate and recent whole-genome comparisons have shown that many chromosomes have remained more or less intact during avian evolution. Here I discuss progress in the development of genetic maps of natural bird populations, which has revealed that the evolutionary stasis of chromosomes often extends to conservation of gene order. The evolutionary stability of bird chromosomes, which might relate to a low frequency of transposable elements, will facilitate the transfer of genomic information from model to non-model organisms and might have a connection to the rarity of postzygotic incompatibilities observed in birds.