Chromosome banding pattern conservatism in birds and nonhomology of chromosome banding patterns between birds, turtles, snakes and amphibians

Abstract

The G-banded karyotypes of 4 species of birds representing the orders Galliformes, Columbiformes and Musophagiformes were compared. Banding pattern homology between orders was limited to 5 major chromosome arms and the Z chromosome. Even in these major chromosome arms pericentric and paracentric inversions produced alteration of the banding pattern sequences. Addition of constitutive heterochromatin was responsible for changes in banding pattern in the Z chromosome. The chromosome banding patterns of an emydid turtle, Terrepene Carolina, 5 species of boid snakes of the genera Liasis, Acrantophis, and Sanzinia and the African clawed-frog, Xenopus muelleri, were also compared to the bird chromosome banding patterns. No homology was observed between any of these major groups: bird, snake, turtle, amphibian. However, intergrouphomology was apparent. — The data obtained do not support reports of broad interordinal direct homology of the macrochromosomes of birds and refutes the idea of a primitive bird karyotype with 3 pairs of “A group” chromosomes and 3 pairs of “B group” chromosomes. — The major mechanisms responsible for chromosome evolution in birds appear to be centric and tandem fusions, paracentric and pericentric inversions, and addition or deletion of heterochromatin.