The Dynamics of Chromosome Evolution in Reptiles

Sauropsida (all existing reptiles and birds) comprises Archosauromorpha (birds, crocodiles, and turtles) and Lepidosauromorpha (tuataras and squamate reptiles). Squamate reptiles have a variable number of chromosomes (2n = 30–50), and their karyotypes are basically categorized into two types: the karyotype with few or no dot-shaped microchromosomes; and the other type consisting of macrochromosomes and many microchromosomes (Olmo and Signorino 2005). This karyotypic feature is also observed in birds and turtles, which comprise a small number of macrochromosomes and a lot of indistinguishable microchromosomes (Belterman and De Boer 1984; Olmo and Signorino 2005). On the contrary, the karyotype of crocodiles contains macrochromosomes with only a few large chromosomes, and the absence of dot-shaped microchromosomes. Comparison of the chromosome maps of Chinese soft-shelled turtle (Pelodiscus sinensis), Siamese crocodile (Crocodylus siamensis), Japanese four-striped rat snake (Elaphe quadrivirgata), and butterfly lizard (Leiolepis reevesii rubritaeniata) with chicken (Gallus gallus) revealed that genetic linkages have been highly conserved between Aves, Testudines, Crocodylia, and Squamata (Matsuda et al., 2005; Matsubara et al., 2006, 2012; Srikulnath et al., 2009a,b; Uno et al., 2012) since the Sauropsida diverged from the Synapsida around 320 millio