Chromosome Polymorphism and Bivalent-forming Triploid and Tetraploid Tradescantia pallida (Commelinaceae)

Abstract

Karyotypes and meiotic chromosome pairing were studied in natural autotriploid and autotetraploid Tradescantia pallida. At both ploidy levels chromosomes appeared as metacentrics, being larger at the triploid than at the tetraploidy level (9.6-15.3 μm and 7.5-10.0 μm, respectively).T. pallida exhibits polymorphism with respect to number and position of secondary constrictions. The tetraploid had three large satellites and a small-spheric one. While the triploid had two large satellites and one small-spheric. Both the triploid and tetraploid showed reduced multivalent pairing for triploid, only one trivalent was seen in 32.8% PMC's while 67.2% PMC's had 6 bivalents plus 6 univalents. In the tetraploid, bivalent pairing was very predominant, 87.72% PMC's had 12 bivalents. The presence of a bivalent-forming system in these polyploids, most probably a genetic one, is suggested.