综述与专论
2010, 32(1): 163-172.
This review gives a historical account of Brassica cytogenetics from chromosome number determination to the recent advancements in molecular cytology. Brassica cytogenetics started with the determination of somatic chromosome number of Brassica rapa (syn. B. campestris) by Japanese researcher N. Takamine. Russian botanist G.D. Karpechenko’s synthesis of Raphanobrassica was an important milestone representing the first example of a new species obtained through experimental hybridization. Japanese scientists Morinaga, and Nagaharu U pioneered genome analysis and unraveled the cytogenetic architecture of crop brassicas. The 1930s witnessed karyotype investigations on somatic chromosomes. Later, pachtene chromosome analysis led G. Röbbelen (1960) to propose the genetic constitution of the basic archetype. Brassica chromosomes are very small and lacking distinctive physical landmarks which makes difficult to generate reliable karyotypes. In recent years, classical cytogenetics has given way to molecular cytogenetics. Molecular karyotypes have been constructed using fluorescence in situ hybridization (FISH) with ribosomal DNA probes with individual chromosomes reliably identified. Since early 1950s, syntheses of natural alloploid species and of late, wide hybridizations between wild and crops species have successfully been carried out taking advantage of recent developments in tissue culture techniques. In early 1980s, the amenability of Brassica species for protoplast regeneration and fusion was demonstrated which enabled the syntheses of a large number of somatic hybrids including a substantial number of intertribal combinations. These experiments extensively helped in expanding the genetic base of existing allopolyploid species and increasing use of related wild germplasm for incorporating new genes which had not been accessible till recently. Comparative genomics between Arabidopsis and Brassica species have elucidated evolutionary processes. At present, Brassica and Arabidopsis regarded as model organisms in the field of experimental biology.
