Highly conserved linkage homology between birds and turtles: Bird and turtle chromosomes are precise counterparts of each other
- 463 Downloads
The karyotypes of birds, turtles and snakes are characterized by two distinct chromosomal components, macrochromosomes and microchromosomes. This close karyological relationship between birds and reptiles has long been a topic of speculation among cytogeneticists and evolutionary biologists; however, there is scarcely any evidence for orthology at the molecular level. To define the conserved chromosome synteny among humans, chickens and reptiles and the process of genome evolution in the amniotes, we constructed comparative cytogenetic maps of the Chinese soft-shelled turtle (Pelodiscus sinensis) and the Japanese four-striped rat snake (Elaphe quadrivirgata) using cDNA clones of reptile functional genes. Homology between the turtle and chicken chromosomes is highly conserved, with the six largest chromosomes being almost equivalent to each other. On the other hand, homology to chicken chromosomes is lower in the snake than in the turtle. Turtle chromosome 6q and snake chromosome 2p represent conserved synteny with the chicken Z chromosome. These results suggest that the avian and turtle genomes have been well conserved during the evolution of the Arcosauria. The avian and snake sex Z chromosomes were derived from different autosomes in a common ancestor, indicating that the causative genes of sex determination may be different between birds and snakes.
Key wordscomparative mapping evolution linkage sex chromosome snake turtle Z-chromosome
Unable to display preview. Download preview PDF.
- Bickham JW, Bull JJ, Legler JM (1983) Karyotypes and evolutionary relationships of trinychoid turtles. Cytologia 48: 177–183.Google Scholar
- Graves JAM, Shetty S (2000) Comparative genomics of vertebrates and the evolution of sex chromosomes. In: Clark MS, ed. Comparative Genomics. Boston, Dordrecht, London: Kluwer Academic Publishers, pp 153–205.Google Scholar
- International Chicken Genome Sequencing Consortium (2004) Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution. Nature 432: 695–716.Google Scholar
- Kumar S, Hedges SB (1998) A molecular timescale for vertebrate evolution. Nature 392: 917–920.Google Scholar
- Sasaki M, Takagi N, Nishida C (1984) Current profiles of avian cytogenetics, with notes on chromosomal diagnosis of sex in birds. The Nucleus 27: 63–73.Google Scholar
- Sato H, Ota H (2001) Karyotype of the Chinese soft-shelled turtle, Pelodiscus sinensis, from Japan and Taiwan, with chromosomal data for Dogania subplana. Cur Herpetol 20: 19–25.Google Scholar