Sources of Chromosomal Polymorphism of Microsporocytes in Species of Lilium L. and Allium L.: Cytomixis, Extra Chromosomes, and Chromatin Diminution

Cytomixis and chromosomal polymorphism of microsporocytes in microsporogenesis of the species Lilium croceum Chaix, Allium fistulosum L., and A. cepa L. were studied. It was found that the main cytomictic events are associated with the early prophase of meiosis and are obligatory (constitutive) for the examined species. In metaphase microsporocytes, the so-called extra chromosomes, presumably of cytomictic origin, were identified. They are characterized by weakening of synapsis and/or disintegration of homologues and associations with bivalents of the basic karyotype with the formation of secondary associations of chromosomes. Extra chromosomes are present not only in hyperchromosomal but also in eu- and hypochromosomal microsporocytes. The majority of extra chromosomes seem to be a “genetic ballast” for the cell, which it gets rid of using a wide range of cellular tools, in particular, chromosomal rearrangements, chromatin diminution, asymmetry of division, cytomixis, and programmed cell death. Nevertheless, some extra chromosomes can participate in the rearrangement of the karyotype of microsporocytes and microspores.