B-CHROMOSOME BEHAVIOR IN MAIZE POLLEN AS DETERMINED BY A MOLECULAR PROBE

The B chromosomes of maize typically undergo nondisjunction during the second microspore division (generative cell division). When the micro spore nucleus contains only one B chromosome, two kinds of sperm resul t, one with two B chromosomes and one with no B chromosomes. The sperm with the B chromosomes preferentially fertilizes the egg cell. Previo us studies of these phenomena have been limited to genetic analysis an d chromosome spreads. In this study we show that a B chromosome-specif ic probe can be used with fluorescence in situ hybridization (FISH) an alysis to detect the presence, location, and frequency of B chromosome s in intact interphase nuclei within mature pollen of maize. Using gen etic line TB-10L18, our results indicate that nondisjunction of the B centromere occurs at an average frequency of 56.6%, based on four plan ts and 1306 pollen grains analyzed. This is consistent with the result s of genetic studies using the same BA translocation. In addition, our results suggest that B chromosome nondisjunction can occur during the first microspore division. Spatial distribution of the B chromosome-s pecific probe appears to be largely confined to one tip of the sperm n ucleus, and a DNA fragment found outside the pollen nuclei often hybri dizes to the B chromosome-specific probe.