Chromosome distribution and catenation in Rhoeo spathacea var. concolor

Abstract

The twelve chromosomes of Rhoeo spathacea variety concolor are arranged in a definite sequence in a ring at meiosis. Identification of all the 12 chromosomes was possible in 119 diakinesis and metaphase I cells. — Pollen viability was measured to be 36.54% by cotton blue staining procedure. Forty five of 56 metaphase I cells (80.36%) had adjacent distribution. Each of the 12 chromosomes was equally likely to be involved in adjacent distribution regardless of their sizes and heterobrachialness. Adjacent distribution occurred randomly at each arm-position in the ring regardless of the lengths of the arm-pairs. — The most frequent chromosome configuration at diakinesis and metaphase I was a chain-of-12 chromosomes (41.18%). Cells with 1 to 4 chains of chromosomes were observed. The observed frequencies of various configurations were in good agreement with the calculated frequencies. The mean number of chiasmata was 10.90 per cell and 0.908 per pair of chromosome arms. The 131 chiasma failures were distributed at random among the 12 arm-positions. Since the lengths of arm-pairs in the ring vary, the randomness may mean that chiasma formation was limited to short terminal segments on all chromosomes.