抄録
At the meiotic prophase of the PMCs in Rhoeo discolor Hance, twelve chromosomes conjugate end-to-end forming a ring, a chain or several chains, a condition which was attributed by Sax (1931) and others to the segmental interchange between non-homologous chromosomes. Non-disjunction of meiotic chromosomes has been observed by several authors to occur with tolerable frequencies. The present author has studied non-disjunction of meiotic chromosomes in connection with the pollen fertility. The observation on 100 metaphase plates which were obtained from acetocarmine preparations showed the following facts.
1) Non-disjunction of adjacent chromosomes in a ring or a chain occurs in about one-third of the pollen mother cells observed (Table 1).
2) The occurrence of such non-disjunction is restricted to relatively long chains (Table 2).
3) Non-disjunction of adjacent kinetochores connected by two short arms occurs more than seven times as frequently as those by long arms (Table 3 and Text-figs. 1-4).
4) Another case of non-disjunction takes place in cases of more than two chains, suggesting that each chain constitutes a system independent of one another regarding chromosome movement (Text-figs. 4-6).
5) Pollen grains which received at least one complete genome are capable of the further nuclear divisions, but those containing less than one genome degenerate soon after the tetrad formation (Text-figs. 7 and 8).
The expectation for the pollen fertility calculated from the present data (Table 4) is approximately close to the actual pollen fertility examined in acetocarmine preparations (Table 5).
Disjunction and non-disjunction of adjacent kinetochores in a ring or a chain must depend upon the behavior of polar granules at diakinesis and metaphase. The investigation on these matters is now in progress.
