一般而言,，易位的非同源染色體在減數分裂中形成異常的“四價體”配對,存在三種分離方式,，可形成6種配子,，由此在后代中出現多種核型個體,。而其中不平衡配子由于遺傳上的缺失和重復引起不育或育性極低,，導致后代種群繁殖力降低,，因而易位多態(tài)在自然群體中極難形成,，在脊椎動物中更是罕見。兩棲類自然種群中,，因易位在種群中引起的核型多態(tài)現象未見報道,。迄今，對于脊椎動物包括兩棲類中易位所引起的細胞學及遺傳學效應知之甚少,。
中國科學院成都生物研究所曾曉茂研究組博士生卿立燕等人自2006年起,，采集了來自33個種群計471號棘腹蛙標本，采用Giemsa染色,、FISH技術及線粒體分子系統(tǒng)學等方法,，初步證實棘腹蛙染色體1號和6號染色體間發(fā)生了相互易位，并在種群中形成了罕見的染色體易位多態(tài)現象,。在種群中共檢測出5類核型：I,，MM/mm；II,，MM/mSt,；III，MT/mm；IV,，MT/mSt,；V，MT/StSt,；其中II,、III和V類核型個體在種群中少見。據此,，推測棘腹蛙易位多態(tài)性是由減數分裂后期易位四價體的對位分離和鄰位-1分離所產生,，且以對位分離為主導，鄰位-1分離頻率低,，無鄰位-2分離,。推測棘腹蛙中相互易位為一次起源，核型IV個體（易位雜合子）在不同種群間的擴散引起了棘腹蛙中豐富的易位多態(tài)現象,?；诰€粒體序列分析，棘腹蛙的發(fā)生易位和未易位的種群形成一個支持率很高的單系, 說明發(fā)生易位的種群和核型正常的種群間并未發(fā)生明顯的遺傳分化,。（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.
