Meiosis was studied in pollen mother cells (PMCs) with 2n=31 in the intergeneric hybrid between Brassica napus L. (2n=38) and Orychophragmus violaceus (L.) O.E. Schulz (2n=24). Three patterns of chromosome behaviour were observed. (Ⅰ) All 31 chromosomes proceeded directly to the second division, giving rise to unreduced gametes. (Ⅱ) Two groups of 12 and 19 chromosomes moved to opposite poles during the first division and produced, after the second division, four daughter chromosomal groups: two with 12 chromosomes and two with 19 chromosomes. Accordingly, these two types of gametes have the same number of chromosomes as found in the gametes produced by the two parental species. They probably contain complete chromosome complements of O. viohweus and B. napus, respectively. (Ⅲ) At anaphase 1, 19 univalents possibly of B. napus origin, moved to the poles in different numbers but most frequently in a 9:10 distribution. Twelve chromosomes, possibly of O. violaceus origin, appeared as six bivalents that lagged behind and were not included in the telophase 1 nuclei. The presumable O. violaceus chromosomes were thus not synchronous with those of B. napus. PMCs with more than 6 bivalents and with univalents at the equatorial plate were the most frequent category observed. There were indications that even in these cells, six bivalents often lagged behind at a later stage. The apparent separation of parental genomes and subsequent formation of pollen with either of the parental genomes (type Ⅱ above) explains the production of plants with 2n=38 of B. napus morphology among the progenies of these hybrids.

In the sexual intergenerie hybrids between the cultivated Brassica species and Orychophragmus violaceus, both complete separation and partial separation of the parental genomes were found to occur during mitosis and meiosis under genetic control. The cytogenetics of these hybrids was species-specific for Brassica parents. The different chromosome behavior of hybrids with three Brassica diploids (B. camtpestris, B. nigra and B. oleracea) might contribute to the different cytogenetics of hybrids with three tetraploids (B. napus, B. juncea and B. carinata). Owing to the parental genome separation, Brassica homozygous plants and aneuploids with various chromosome constitutions were identifiable in the progenies of these hybrids, which were valuable for the study of the structure and evolution of Brassica genome and for the breeding of Brassica crops.