一般而言，易位的非同源染色体在减数分裂中形成异常的“四价体”配对,存在三种分离方式，可形成6种配子，由此在后代中出现多种核型个体。而其中不平衡配子由于遗传上的缺失和重复引起不育或育性极低，导致后代种群繁殖力降低，因而易位多态在自然群体中极难形成，在脊椎动物中更是罕见。两栖类自然种群中，因易位在种群中引起的核型多态现象未见报道。迄今，对于脊椎动物包括两栖类中易位所引起的细胞学及遗传学效应知之甚少。
中国科学院成都生物研究所曾晓茂研究组博士生卿立燕等人自2006年起，采集了来自33个种群计471号棘腹蛙标本，采用Giemsa染色、FISH技术及线粒体分子系统学等方法，初步证实棘腹蛙染色体1号和6号染色体间发生了相互易位，并在种群中形成了罕见的染色体易位多态现象。在种群中共检测出5类核型：I，MM/mm；II，MM/mSt；III，MT/mm；IV，MT/mSt；V，MT/StSt；其中II、III和V类核型个体在种群中少见。据此，推测棘腹蛙易位多态性是由减数分裂后期易位四价体的对位分离和邻位-1分离所产生，且以对位分离为主导，邻位-1分离频率低，无邻位-2分离。推测棘腹蛙中相互易位为一次起源，核型IV个体（易位杂合子）在不同种群间的扩散引起了棘腹蛙中丰富的易位多态现象。基于线粒体序列分析，棘腹蛙的发生易位和未易位的种群形成一个支持率很高的单系, 说明发生易位的种群和核型正常的种群间并未发生明显的遗传分化。（生物谷Bioon.com）
doi:10.1371/journal.pone.0046163
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A De Novo Case of Floating Chromosomal Polymorphisms by Translocation in Quasipaa boulengeri (Anura, Dicroglossidae)
Liyan Qing, Yun Xia, Yuchi Zheng, Xiaomao Zeng
Very few natural polymorphisms involving interchromosomal reciprocal translocations are known in amphibians even in vertebrates. In this study, thirty three populations, including 471 individuals of the spiny frog Quasipaa boulengeri, were karyotypically examined using Giemsa stain or FISH. Five different karyomorphs were observed. The observed heteromorphism was autosomal but not sex-related, as the same heteromorphic chromosomes were found both in males and females. Our results indicated that the variant karyotypes resulted from a mutual interchange occurring between chromosomes 1 and 6. The occurrence of a nearly whole-arm translocation between chromosome no. 1 and no. 6 gave rise to a high frequency of alternate segregation and probably resulted in the maintenance of the translocation polymorphisms in a few populations. The translocation polymorphism is explained by different frequencies of segregation modes of the translocation heterozygote during meiosis. Theoretically, nine karyomorphs should be investigated, however, four expected karyotypes were not found. The absent karyomorphs may result from recessive lethal mutations, position effects, duplications and deficiencies. The phylogenetic inference proved that all populations of Q. boulengeri grouped into a monophyletic clade. The mutual translocation likely evolved just once in this species and the dispersal of the one karyomorph (type IV) can explain the chromosomal variations among populations.
