Studies on the control of diploid-like meiosis in polyploid taxa of Chrysanthemum. I. Hexaploid Ch. japonense Nakai.

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Abstract
In meiosis of C. japonense (Saka strain) 2n = 6x = 54, 27 II was the main chromosome configuration and 1 IV + 25 II and 26 II + 2 I were rarely observed. Fifty-four chromosomes, at mitotic metaphase, varied in length from 8.4-4.2 .mu.m and in arm ratio from 1.0-4.9. Ten satellite chromosomes and 6 small chromosomes with extreme subterminal centromeres were well distinguishable. Karyomorphologically this species is not an autohexaploid. Apparently, chromosome pairing is initiated at 2 sites, A and B; they are under the independent and fundamentally different control, respectively. At either site pairing is always 2-by-2, with the pairing initiated at the A site being independent of that initiated at the B site. The initiation of pairing at the A site always precedes that at the B site. The initiation of pairing at the B site is usually suppressed by the multiple or poly-genic control. This genetic system must ensure the diploid-like meiosis in hexaploid C. japonense although all of the constituent genomes of this species are sufficiently homologous to be able to pair with each other. The magnitude of release from the suppression of the initiation of pairing at the B site depends on either the reduction of suppressive gene dosage or the interference of the lonely chromosome, without the essentially homologous pairing partner in odd-ploids. The magnitude of release from the suppression is equal, not preferential at each B site.