Istituto di Biologia e Genetica, Università Politecnica delle Marche and Istituto Nazionale di Biosistemi e Biostrutture, Via Brecce Bianche, 60131 Ancona, Italy.
Integr Comp Biol. 2008 Oct;48(4):486-93. doi: 10.1093/icb/icn049. Epub 2008 Jun 2.
Reptiles are a karyologically heterogeneous group, where some orders and suborders exhibit characteristics similar to those of anamniotes and others share similarities with homeotherms. The class also shows different evolutionary trends, for instance in genome and chromosome size and composition. The turtle DNA base composition is similar to that of mammals, whereas that of lizards and snakes is more similar to that of anamniotes. The major karyological differences between turtles and squamates are the size and composition of the genome and the rate at which chromosomes change. Turtles have larger and more variable genome sizes, and a greater amount of middle repetitive DNA that differs even among related species. In lizards and snakes size of the genome are smaller, single-copy DNA is constant within each suborder, and differences in repetitive DNA involve fractions that become increasingly heterogeneous with widening phylogenetic distance. With regard to variation in karyotype morphology, turtles and crocodiles show low variability in chromosome number, morphology, and G-banding pattern. Greater variability is found among squamates, which have a similar degree of karyotypic change-as do some mammals, such as carnivores and bats-and in which there are also differences among congeneric species. An interesting relationship has been highlighted in the entire class Reptilia between rates of change in chromosomes, number of living species, and rate of extinction. However, different situations obtain in turtles and crocodiles on the one hand, and squamates on the other. In the former, the rate of change in chromosomes is lower and the various evolutionary steps do not seem to have entailed marked chromosomal variation, whereas squamates have a higher rate of change in chromosomes clearly related to the number of living species, and chromosomal variation seems to have played an important role in the evolution of several taxa. The different evolutionary trends in chromosomes observed between turtles and crocodiles on the one hand and squamates on the other might depend on their different patterns of G-banding.
爬行动物在核型上具有异质性，其中一些目和亚目具有类似于无羊膜动物的特征，而另一些则与恒温动物具有相似之处。该类群还表现出不同的进化趋势，例如在基因组和染色体大小和组成上。龟类的 DNA 碱基组成与哺乳动物相似，而蜥蜴和蛇类则与无羊膜动物更为相似。龟类与有鳞目之间的主要核型差异在于基因组的大小和组成以及染色体变化的速度。龟类具有更大和更可变的基因组大小，以及更多的中重复 DNA，即使在相关物种之间也存在差异。在蜥蜴和蛇类中，基因组的大小较小，每个亚目内的单拷贝 DNA 是恒定的，而重复 DNA 的差异涉及到随着系统发育距离的扩大而变得越来越不均匀的分数。就核型形态的变异而言，龟类和鳄类的染色体数目、形态和 G 带模式的变异性较低。在有鳞目动物中发现了更大的变异性，它们的核型变化程度与一些哺乳动物（如食肉动物和蝙蝠）相似，并且在同属物种之间也存在差异。在整个爬行动物类群中，已经强调了染色体变化率、现存物种数量和灭绝率之间的有趣关系。然而，龟类和鳄类与有鳞目动物之间存在不同的情况。在前者中，染色体变化的速度较低，并且各种进化步骤似乎并没有导致明显的染色体变异，而有鳞目动物的染色体变化速度较高，这显然与现存物种的数量有关，并且染色体变异似乎在几个分类单元的进化中发挥了重要作用。龟类和鳄类与有鳞目动物之间在染色体进化趋势上的差异可能取决于它们不同的 G 带模式。
