The mechanisms behind the regular segregation of the m‐chromosomes in Coreus marginatus L. (Coreidae, Hemiptera)

Abstract

Meiotic behaviour of m‐chromosomes in Coreus marginatus L. males and females was reinvestigated using improved cytological methods. In male meiosis, synapsis of the m‐chromosomes was found to be normal. In part of the meiocytes, desynapsis leads to the occurrence of m‐chromosome univalents. Univalent m‐chromosomes congregate separately and, after their lateral movement from the periphery to the center of the radial metaphase plate, they undergo touch and go pairing during the stabilization of metaphase configuration. The observations made suggest that the determination of segregation of univalent m‐chromosomes (i. e., their correct initial orientation to opposite poles) and touch and go pairing are sequential but separate events, the latter being attributable to the formation of the radial metaphase plate. A model explaining the correct initial orientation of univalent m‐chromosomes is forwarded. According to the model, the movement of m‐chromosomes after desynapsis is nonrandom and results in the m‐chromosomes being positioned on the nuclear membrane in such a manner that they will orientate initially to different spindle poles. The behaviour of autosomal bivalents and m‐chromosome univalents during prometaphase suggests a new model for the formation of radial metaphase configuration. According to the model, touch and go pairing of the m‐chromosomes is a result of those factors which determine the stabilized positions of different chromosomes on the metaphase plate. In female meiosis and in part of the cells in male meiosis, chiasma formation ensures the regular segregation of the m‐chromosomes. Evidently, the regular behaviour of the m‐chromosomes during meiosis is ensured by two basically different mechanisms. Copyright © 1986, Wiley Blackwell. All rights reserved