The absence of chiasma terminalization and inverted meiosis in males and females of Myrmus miriformis Fn. (Corizidae, Heteroptera).

摘要

Terminalization of chiasmata and orientation of bivalents were analysed in males and females of Myrmus miriformis, using insects collected from the field in Turku, Finland. In spermatogenesis, the frequencies of the largest autosome bivalent with medial, subterminal and terminal chiasmata were compared at diplotene, early and late diakinesis and metaphase I. The bivalent displayed a single subterminal or medial chiasma in nearly 90% of cells at diplotene. The frequency of such bivalents was still >80% at metaphase I, indicating the absence of complete chiasma terminalization. It is possible that chiasmata do not terminalize at all. In oogenesis, all bivalents at metaphase I displayed subterminal or medial chiasmata, indicating that terminalizationis also absent in females. In both males and females all bivalents co-orientated at metaphase I, the telomeres of homologous chromosomes being orientated towards opposite spindle poles. Hence, they underwent prereduction in meiosis and no evidence for an inverted meiosis could be found.