STUDIES ON TRIPLOID ALLIUM-TRIQUETRUM .2. METAPHASE-I UNIVALENTS AND THEIR INFLUENCE ON ANAPHASE-I DISTRIBUTION

The relationship between the univalents seen at metaphase I and the distribution of dyads at anaphase I in the pollen mother cells of triploid A. triquetrum are described. The orientation of the centromeres within the trivalents and bivalents at metaphase I towards the 2 poles of the pollen mother cells is random. The distribution of polar univalents towards the 2 poles at metaphase I is also random, as is the distribution of dyads at anaphase I in "low" univalent frequency collections. However, in a "high" univalent frequency collection, the distribution of dyads at anaphase I is non-random. There is an excess of cells with the most equal dyad distribution (13-14) and a paucity of cells with a 12-15 distribution. In low univalent frequency collections, the equatorial univalents are believed to remain in the equatorial region during anaphase I and are seen as laggards at late anaphase I. The remaining chromosomes move according to the metaphase I orientation of their centromeres to give a random distribution of dyads at anaphase I. In high univalent frequency collections it is argued that the non-random dyad distribution seen at anaphase I is the result of non-random movement of some of the equatorial univalents away from the equatorial region during anaphase I. The remaining equatorial univalents remain in the equatorial region and are seen as laggards at late anaphase I.