[Objective] This study aimed to compare the similarities and dissimilarities in karyotypes of purple and white onions, so as to lay foundation for further studying its genetic improvement and breeding more onion varieties. [ Method] Sections of root-tip cells were prepared by normal wafer method. Photomicrography was adopted to produce the high-quality chromosome specimen. Finally, karyotype analysis was conducted using Adobe Photoshop [ Result ] Chromosome karyotype analysis on the root-tip showed that the chromosome number of both purple and white onions was 2n = 2x = 16. Among the 16 chromosomes of both the onions, no satellite chromosome was found. By measuring and calculating, it was found that the karyotype of the studied white union belonged to the lowly evolutional 2A type, and its karyotype formula was 2n = 2x = 16 = 14 m + 2St, with the karyotype asymmetry coefficient of 58. 67% . No obvious centromere was observed in the sections of purple onion. [ Conclusion] The karyotypes of white and purple unions are similar and we can infer from this fact that the reason of different characters between both the onions is not due to the chromosome aberration. This karyotype formula and asymmetrical karyotype coefficient had spme reference values on the identification of onion variety resources.%[目的]分析紫色洋葱和白色洋葱的核型并比较他们的异同点,为进一步研究洋葱遗传改良奠定基础,为培育洋葱新品种提供理论依据.[方法]运用传统的压片技术制备洋葱根尖细胞染色体标本后进行核型分析.[结果]通过对紫色洋葱和白色洋葱根尖细胞的核型分析,发现2种洋葱的染色体数均为2n=2x=16,其中均未发现具有随体的染色体.通过对白色洋葱的染色体进行测量和计算发现其核型均属进化程度较低的2A型,核型公式为2n =2x=16=14m +2St(SAT),核型不对称系数58.67％；而紫色洋葱的染色体制片由于无明显着丝粒,故有待于进一步的研究.[结论]2种洋葱的核型相似,说明两者的性状差异不是由染色体变异造成的,需要做进一步的研究；该试验得到的核型公式及核型不对称系数对我国洋葱品种资源的系统分类和遗传育种研究具有一定的参考价值.
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