XVI International Botanical Congess

The B chromosomes of maize typically undergo nondisjunction during the second microspore division. When the microspore contains only one B chromosome, two kinds of sperm result, one with two Bs and one with no Bs. The sperm with the Bs preferentially fertilizes the egg cell. We used fluorescence in situ hybridization (FISH) to detect the frequency of B chromosomes in sperm nuclei. Our results on nondisjunction rates are consistent with those of genetic studies. The B-specific probe is largely confined to one tip of the sperm nucleus. In pollen tubes we found that the sperm containing the B-specific probe did not travel consistently behind or ahead of the other sperm. We have used FISH to identify the two sperm types within populations of isolated sperm. It should now be feasible to use flow cytometry to sort the cells for comparative analyses at the biochemical and molecular levels.