Schmid M, Haaf T, Geile B, Sims S
Chromosoma. 1983;88(1):69-82. doi: 10.1007/BF00329505.
The mitotic and meiotic chromosomes of the marsupial frog Gastrotheca riobambae were analysed with various banding techniques. The karyotype of this species is distinguished by considerable amounts of constitutive heterochromatin and unusual, heteromorphic XY sex chromosomes. The Y chromosome is considerably larger than the X chromosome and almost completely heterochromatic. The analysis of the banding patterns obtained with GC- and AT-base-pair-specific fluorochromes shows that the constitutive heterochromatin in the Y chromosome consists of at least three different structural categories. The only nucleolus organizer region (NOR) of the karyotype is localized in the short arm of the X chromosome. This causes a sex-specific difference in the number of NOR: female animals have two NORs in diploid cells, male animals one. No cytological indications were found for the inactivation of one of the two X chromosomes in the female cells. In male meiosis, the heteromorphic sex chromosomes form a characteristic sex-bivalent by pairing their telomeres in an end-to-end arrangement. The significance of the XY/XX sex chromosomes of G. riobambae for the study of X-linked genes in Amphibia, the evolution of sex chromosomes and their specific DNA sequences, and the significance of the meiotic process of sex chromosomes are discussed.
利用多种显带技术对袋蛙（Gastrotheca riobambae）的有丝分裂和减数分裂染色体进行了分析。该物种的核型特征是含有大量的组成型异染色质以及异常的异形XY性染色体。Y染色体比X染色体大得多，几乎完全是异染色质。对用GC和AT碱基对特异性荧光染料获得的带型分析表明，Y染色体中的组成型异染色质至少由三种不同的结构类别组成。核型中唯一的核仁组织区（NOR）位于X染色体的短臂上。这导致NOR数量存在性别特异性差异：雌性动物的二倍体细胞中有两个NOR，雄性动物有一个。未发现雌性细胞中两条X染色体之一失活的细胞学迹象。在雄性减数分裂中，异形性染色体通过端对端排列配对其端粒，形成特征性的性二价体。讨论了袋蛙的XY/XX性染色体对于两栖动物X连锁基因研究、性染色体进化及其特定DNA序列的意义，以及性染色体减数分裂过程的意义。
