Meiotic behaviour of a new complex X-Y-autosome translocation and amplified heterochromatin in Jumnos ruckeri (Saunders) (Coleoptera, Scarabaeidae, Cetoniinae).
Species belonging to the Cetoniinae subfamily studied so far possess 20 chromosomes, including a small X and a punctiform Y: 20,Xyp in the males. In a series of species from the Goliathini tribe under study we found a very unusual karyotype, with 12 autosomes and large sex chromosomes (14,neoXY) in Jumnos ruckieri from Thailand. Applying various techniques including pachytene bivalent spreading, we showed that 40% (mitotic and meiotic prophases) to 60% (metaphases) of the karyotype length was composed of heterochromatin. Both sex chromosomes were NOR carriers. At pachynema they underwent a complete synapsis of their distal regions, indicating their autosomal origin. At contrast, their very uneven central regions remained separated, but associated with nucleolus material. This association persisted until diakinesis, forming a pseudo-chiasma between the neoX and the neoY, which were always in end-to-end association. Compared to free autosomes the autosomal parts of the neo-sex chromosomes had a significant lack of interstitial chiasmata, indicating a possible lack of recombination at their proximal regions. As in the cases of X-autosome translocations in mammals, autosomal and gonosomal parts of the neo-sex chromosomes were insulated by heterochromatin, which may be a necessary condition to avoid deleterious position effects, whatever the mechanisms of gene dosage compensation.
Macaisne
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UMR 5202 CNRS/MNHN, Organisation, Structure et Evolution de la Biodiversité, Muséum National d'Histoire Naturelle, CP 39, 16, rue Buffon, Paris, 75005, France.
Dutrillaux
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AM
Dutrillaux
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B
D000818:Animals; D001517:Coleoptera / Q000235:genetics*; D006570:Heterochromatin / Q000235:genetics*; D008297:Male; D008540:Meiosis / Q000235:genetics*; D008938:Mitosis / Q000235:genetics; D009697:Nucleolus Organizer Region / Q000648:ultrastructure; D014178:Translocation, Genetic; D014960:X Chromosome / Q000235:genetics*; D014998:Y Chromosome / Q000235:genetics*
D006570:Heterochromatin