Induced asynaptic mutants in Vicia faba L.

Abstract

Eleven induced asynaptic mutants of Vicia faba L. were investigated. The mutagens employed were neutrons, gamma rays, EMS, and EMS + Cu++. The mutants are designated as asynaptic on the basis of the terminology of Soost. According to the classification of Prakken, one of the mutants displays weak asynapsis, one complete, and the others medium‐strong asynapsis. The behaviour of the mutants at metaphase I has received particular attention. Based on the correlation between chromosome length and univalent frequency, with two exceptions, the asynaptic genes influenced the long chromosome more than the short ones. The long chromosome, although about twice the size of the shorter chromosomes, formed univalents almost as frequently as any of the short chromosomes. The asynaptic genes – as expected – also have a negative effect on the chiasma frequency of the remaining bivalents. Except for one mutant, the reduction of chiasmata exceeded 50 per cent. Contrary to most other reported cases of asynapsis, chiasma reduction occurred at random within the chromosomes. Chiasma reduction was more accentuated in the long chromosome than in the short chromosomes, thus resulting in nearly equal chiasma frequencies for all the chromosomes except in the single mutant displaying weak asynapsis. The chiasma frequency per bivalent was independent of number of bivalents per cell aside from one mutant. No dividing univalents were observed in anaphase I. Finally, the regularity of the second division is dependent on the frequency of lagging univalents in anaphase I. 1970 Hereditas