STUDIES ON TETRAPLOID RICE:V. THE BEHAVIOR OF CHROMOSOMES IN THE MEIOSIS OF TETRAPOLOID RICE VARIETIES AND THEIR HYBRIDS

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1. A number of tetraploid rice varieties and their F1 hybrids were observed with regard to the behavior of chromosomes in pollen mother cells. It was found that in a greater part of cells every four homologus chromosomes formed either one quadrivalent or two bivalents, but a few univalents were also seen.2. The average number per cell of quadrivalent and bivalent chromosomes differed with the variety or in hybrids with the combination of varieties, and ranged from 5 to 9 or from 5 to 12 respectively.3. It was generally found that in intervarietal hybrids the numbers of quadri- and univalent chromosomes were less numerous than in auto-tetraploid varieties. Numerically unequal division at anaphase was also less frequent in hybrids. However, hybrids between mutually remote varieties and between close ones showed no significant difference in this tendency.4. Hybrids were generally higher in fertility. Among the hybrids or the parental varieties, no significant correlation was found between the number of quadri- or univalent chromosomes and fertility.5. The improvement of chromosome behavior in hybrids may be due either to selective pairing of chromosomes derived from the same parent or to a complementary effect of parental genes. It seemed difficult, however, to evaluate the relative probability of these two hypotheses from these cytological data.
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