MEIOSIS IN PROTISTS - RECENT ADVANCES AND PERSISTING PROBLEMS

This review summarizes the results obtained on meiosis in protists in the last 14 years. Special attention is drawn to the discovery of sexual phenomena in protozoan groups which were earlier considered asexual and to the rather widespread occurrence among the protists of heterophasic life cycles (with ''intermediate'' meiosis). Synaptonemal complexes are considered markers of early parallel chromosome pairing which is typical of two-divisional meiosis. Two-divisional meiosis (though sometimes achiasmatic) seems to be the general rule among protists, including the Apicomplexa and the dinoflagellates. One-divisional meiosis seems to be rather a rarity having independent and secondary origin (in some flagellates from the gut of Cryptocercus). These cases need reinvestigation with modern methods.