In this study, somatic chromosomes were counted and karyotypes were determined in 13 plants from a population of Allium macrostemon Bunge. (1)Three were heptaploid with karyotype 2n=7x = 46m (2SAT) + 10sm(2SAT) and 2B karyotype of stebbins,ten were tetraploid with 2n=4x=26m(1SAT)+ 6sm(lSAT) and 2B karyotype. Mixoploidy and heptaploid were reported for the first time. (2)It can be inferred that the heptaploid plants was produced via an unreduced gamete of the triploid united with an unreduced gamete of the tetraploid. The number of satellites does not match the ploidy of plants and satellites are not necessarily attached to homologues. The infraspecific ploidy increase is consistent with species evolution, the higher ploidy,the more advanced population.%该试验对浙江大罗山一个薤白种群的13个个体进行了染色体计数和核型分析,并对探讨七倍体薤白的可能形成机制进行了讨论.结果表明:(1)大罗山薤白种群为混倍种群,其中3个个体为七倍体,染色体组型是2n=7x=46m(2SAT)+ 10sm(2SAT),核型为2B型;10个个体为四倍体,染色体组型是2n=4x=26m(1SAT)+6sm(1SAT),核型为2B型.薤白种群的混倍性和七倍体均为首次报道.(2)对七倍体薤白的成因分析认为,七倍体是通过三倍体和四倍体未减数配子结合产生;随体染色体数目并不与植株的倍性相对应,而且并不都是出现于同源染色体上;薤白种内倍性增大与其物种进化的趋势一致,即倍性越大,种群越进化.
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