Comparison of chromosome BrdU-Hoechst-Giemsa banding patterns of the A1 and (AD)2 genomes of cotton

The karyotypes of diploid cotton, Gossypium herbaceum L. var. africanum (Watt) Mauer, and tetraploid cotton, Gossypium barbadense L., were studied by BrdU-Hoechst-Giemsa banding, using a specially developed image-analysis system. The patterns obtained are represented by the slightly and intensively stained bands that correspond, respectively, to the early replicating DNA and the DNA replicating in the mid and late S period. The number of main Giemsa-positive bands varies from 2 to 9 per chromosome. The banding patterns of all homologous pairs are specific in both the A 1 and (AD) 2 genomes. This made possible the complete classification of the chromosomes. Based on the similarity of the BrdU-Hoechst-Giemsa banding patterns and the sizes of the chromosomes in the A 1 and (AD) 2 genomes, we divided the (AD) 2 genome into A b and D b subgenomes and classified their chromosomes according to the A 1 genome chromosome classification. The BrdU-Hoechst-Giemsa banding pattern of the D b subgenome is basically similar to that of the A 1 genome and A b subgenome, but the differences between it and the banding patterns of the A 1 genome and A b subgenome are more significant than the differences between the latter two genomes. The similarity of the intragenomic banding patterns between nonhomologous chromosomes a and b, c and g, d and e, f and j, h and i, and l and m was revealed. Based on our results, we suggest that the ancestral cotton genome contained 7 homologous pairs of chromosomes. The results prove the feasibility of image-analysis techniques for identification and quantitative analysis of chromosomes, especially with regard to small-chromosome species.Key words: cotton, A 1 and (AD) 2 genomes, chromosome identification, BrdU-Hoechst-Giemsa banding, image analysis.