Genomic in situ hybridization (GISH) of Tripsacum dactyloides and Zea maysssp mays with B chromosomes

Genomic affinities between Tripsacum dactyloides (2n = 72) and Zea mays ssp . mays (2n = 20 + 5 B) were analyzed through GISH (genomic in situ hybridiz ation) to ascertain the degree of chromosome homology between the two gener a. Mitotic cells of T. dactyloides were simultaneously probed with total ge nomic DNA from Z. mays ssp. mays (2n = 20) and with rDNA (pTA71). A dispers e pattern of hybridization signal among all 72 chromosomes, corresponding t o maize total DNA, and six strong fluorescent signals due to the rDNA probe hybridizing on 3 chromosome pairs of T. dactyloides were observed. Mitotic chromosomes from Z. mays ssp, mays (2n = 20 + 5 B) were hybridized with a maize line that lacked B chromosomes and knobs and with total DNA from T. d actyloides. The knobless line of maize hybridized intensely on all chromoso mes except for some regions where the probe bound less. Tripsacum dactyloid es bound intensely on one terminal region of each B chromosome and to some regions of chromosome pairs 2, 6, and 8. These regions are DAPI positive an d coincide with regions that displayed lower affinity with the probe from t he knobless maize line. The possible significance of these results is discu ssed briefly.