Cytogenetics of Sorghum. I. The Orientation of Interchange Complexes and Quadrivalents at Metaphase I in S. purpureo-sericeum

Abstract

1. The orientation of two ring interchange complexes in Sorghum purpureosericeum Aschers. et Schweinf. is apparently not directed, since the open and zigzag configurations at metaphase I occur with approximately equal frequencies. 2. The number, type (chain or ring), and orientation (open, zigzag, or straight) of quadrivalents at metaphase I in an autotetraploid (4n + 1) plant of S. purpureo-sericeum were determined. Approximately 40% of the quadrivalents were chains; 75% of the pollen mother cells had 2 or 3 quadrivalents. The orientation of both chain and ring quadrivalents at metaphase I was apparently not directed, since the open and zigzag configurations occurred with approximately equal frequencies. 3. These observations support the hypothesis that, if a species does not display a directed orientation of the chromosomes in an interchange complex at metaphase I, the quadrivalents of an induced or spontaneous autotetraploid of this species will likewise not display a directed orientation at the same s...