Leymus racemosus (Lam.)Tzvel in 5 populations in Altay area chromosome of different popu-lations were observed with optical microscope,at the same time,the chromosome of different individuals from the same population were investigated.The data observed between populations were investigated.The data observed between populations and within the same population were analyzed.The result indicated that chromosome kiaryotype from the 5 populations were homologous to one anather.The karyotype model be-long to 2A.The karyotype formulae were as follows:P1:2n =4x =28=24m (2SAT)+4sm(2SAT);P4:2n =4x =28=20m(2SAT)+8sm;P5:2n =4x =28=20m+8sm(2SAT),and the others:P2:2n =4x =28=26m+2sm;P3:2n =4x =28 =22m+6sm.The differences from 5 different populations lies in whether there were satellite or not,but also in armratio,ratio of chromosome length and asymmetry index.The kar-yotype formulae within the population were as follows:2n = 4x = 28 = 22m + 6sm,belong to 2A among which there are 1 1 pairs of metacentric chromosomes of submetacentric chromosome in the middle and 3 pairs of metacentric chromosomes in nearly middle.There were no satellite,their karyotype belong to 2A. The result showed that there were some changes of karyotype in the Leymus racemosus (Lam.)Tzvel with different populations in Altay area.However,there were a few differences in karyotype formulae.The result indicated that there some changes in different populations of Leymus racemosus (Lam.)Tzvel.The results indicated that there were some changes of karyotype in the Leymus racemosus (Lam.)Tzvel with different populations of Altay area.However,there were a few differences in karyotype formulae.%以新疆阿勒泰地区5个居群的大赖草为材料,采用光学显微镜观察了各居群材料的染色体,同时又观察了一个居群内不同个体的染色体,对观测所得数据进行了居群间和居群内的核型分析.结果显示,5个居群的染色体核型相似,核型类型都属于2A 型,其中3个居群有随体,核型公式分别为：居群1(P1)：2n ＝4x ＝28＝24m (2SAT)＋4sm(2SAT)、居群4(P4)：2n ＝4x ＝28＝20m(2SAT)＋8sm 及居群5(P5)：2n ＝4x ＝28＝20m＋8sm (2SAT),其余2个居群核型公式分别为：居群2(P2)：2n ＝4x ＝28＝26m＋2sm 和居群3(P3)：2n ＝4x ＝28＝22m＋6sm.5个不同居群的差别不仅在随体的有无上,平均臂比、染色体长度比和不对称系数指标上也存在差异.居群内核型公式为：2n ＝4x ＝28＝22m＋6sm,其中中部着丝粒染色体11对,近中部着丝粒染色体3对,无随体,核型类型均为2A 型.结果表明,新疆阿勒泰地区不同居群大赖草在核型上发生了一定的变化,而居群内核型差异较小.
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