Genomic in situ hybridization (GISH) of Brassica juncea (AABB) with biotin-labelled DNA of B-nigra (BB)

Genomic in situ hybridization (GISH) was used to distinguish between chromosomes of closely related Brassica species. Brassica juncea (AABB) was hybridized with a biotin-labelled DNA probe of B. nigra (BB). Brassica nigra (BB) was pre-hybridized with DNA of B. napus (AACC). As a consequence, all common DNA sequences of the BE and AACC genome hybridized and were blocked for further hybridization with the chromosomes of B. juncea (AABB), i.e. only species-specific sequences of B. nigra (BB) were left single stranded, and could hybridize with complementary DNA of B genome in B, juncea (AABB). Streptavidin conjugated to FITC was used to make the genomic hybridization visible under fluorescence microscopy. Whole chromosomes were labelled and AA and BE chromosomes of B. juncea could be distinguished, which has not been possible for Brassica with banding methods. Species crosses are possible and common in Brassica. With GISH addition and substitution lines, large enough translocations and also meiotic pairing of species crosses can be analysed.