Sex chromosomes at early meiosis in three wood mice species of the genus Apodemus (Rodentia, Muridae)

The prophase of the first meiotic division was studied in field mice of the species Apodemus (Sylvaemus) flavicollis, A. (S.) ponticus, and A. (S.) uralensis by light and electron microscopy. The karyotypes of the species were described on the base of electron microscopy of synaptonemal complexes in spermatocytes I. The axial elements of the sex chromosomes at early-middle pachytene can synapse along the major portion of the Y axis; at late pachytene-early diplotene, the synapsis region shrinks; and at diakinesis-metaphase I, X and Y chromosomes associate tail-to-tail in all species studied. The behavior of sex chromosomes in the synapsis in the species studied was quite uniform. The results are discussed in the context of earlier data on the behavior of sex chromosomes in various rodent species in meiosis prophase I and their banding.