棕色田鼠罗伯逊易位的研究(简报)

STUDIES ON THE ROBERTSONIAN TRANSLOCATION OF MICROTUS MANDARINUS

棕色田鼠(Microtus mandarinus Milne-Edwards,1871)又称北方田鼠,主要分布于我国。前苏联、蒙古的少数地区亦有分布,前苏联学者称该鼠为中国田鼠。关于该鼠的染色体研究国内外已有报道。仅推测罗伯逊易位是引起该鼠第一对常染色体多态及其染色体数目多态的主要原因。本文详细研究了该鼠第一对常染色体多态类型与个体染色体数目之间的一一对应关系、性个体(2n=51)的G带带型及其联会复合作中三价体的存在。

The type of chromosome No. 1 and chromosome number from 53 individuals of Microtus mandarinus have been studied and compared in three sex types: XY,XX,XO. We found that the first pair of autosomes are very unstable, and there are three types; (1) M. M (With a double metacentric chromosome), (2)M,T,T, (With single metacentric chromosome). (3)T.T.T.T (Without metacentric chromosome). The chromosome number of the same sex individuals changes regularly with the type change of chromosome No. 1, that is, the increase of one chromosome in 2n number is always accompanied by the increase of two T and the decrease of one M, and vice versa. The synaptonemal complexes (SCs) of spermatocyte in pachytene nuclei from the males (2n = 51) were analysed by the electron microscopy. The SCs studies demonstrate that there are 23 fully paired autosomal bivalents, XY-bivalent and an autosomal trivalent. This trivalent is formed by one metacentric and two telocentric elements and characterized by the presence of two short side-arms. Meanwhile, all trivalents are in a cis configuration. The study of G-bariding also demonstrates that the No. 1 auto-some polymorphism is caused by Robertsonian translocation. Robertsonian fission is the main reason of the polymorphism of chromosome No. 1 and of variation of chromosome number in M. mandarinus.