Abstract:

【Objective】 The aim of this experiment is to localize 5S rDNA on the chromosomes of Brassica oleracea var. acephala by FISH (fluorescence in situ hybridization) and estimate the copy number of 5S rDNA, further provide a basis for the location of genes and the construction of cytogenetic map of chromosome 2 by FISH. 【Method】 B. oleracea var. acephala was used as the experimental material, 5S rDNA probe was labeled by PCR-DIG(PCR-digoxigenin). By FISH, 5S rDNA probe was located on the metaphase chromosomes of tapetal cell, pachytene chromosomes and extended DNA fibers (EDF). 【Result】 In the metaphase chromosomes of tapetal cell and pachytene chromosomes, it was observed that three closely adjacent 5S rDNA hybridization signal sites (a, b, c) located near the centromere in the long arm of the submetacentric chromosome 2, the intensity of signals is b＞a＞c. In the extended DNA fibers, it was estimated that the physical size of three different stretches of beads-on-string (a, b, c) is of the order of 257 kb, 359 kb, and 134 kb, respectively. 【Conclusion】 It was proved that B.oleracea var. acephala contains three tandem repeat sites, and estimated that the copies number of three 5S rDNA locus are about 510, 712, and 266, respectively.

Key words: Brassica oleracea var. acephala, 5S rDNA, fluorescence in situ hybridization (FISH)