Pseudo-Quadrivalents in Autotetraploid Rice

Abstract

IN the course of a statistical examination of chromosome pairing in PMC's of various induced tetraploid forms of Oryza sativa, I have found a regular decrease of the quadrivalent frequency from diakinesis to metaphase I. For 533 cells observed at diakinesis and 741 at metaphase, the mean numbers of quadrivalents per cell were respectively 7.61 and 6.25 : this reduction (18 per cent) is very significant. Together with the reduction of quadrivalent frequency, a complementary increase in the number of bivalents (from 8.63 to 11.01) was noticed. A few uni- and tri-valents were also present at diakinesis (on an average 0.15 and 0.05 per cell) and their number increased up to metaphase (respectively 0.47 and 0.17). These observations showed that some quadrivalents became dissociated before anaphase; they generally gave rise to two bivalents, but sometimes to one trivalent and one univalent or one bivalent and two univalents.