Induced paracentric and pericentric inversions in Vicia faba L.

Abstract

One paracentric and two pericentric inversions, all in chromosome 1, have been investigated in Vicia faba L. The paracentric inversion, constituting about 15–20 per cent of the length of chromosome 1, is recognizable at mitotic metaphase, since the inverted segment is asymmetrical around the secondary constriction between the short arm and the satellite. The frequencies of configurations at anaphase I and anaphase II have been determined. The discrepancy in the frequencies between the two stages is believed to be due to the simultaneous type of pollen formation. Comparisons of data from anaphase I, the tetrad stage, and pollen fertility exhibited good agreement. The inverted segments in the two pericentric inversions constitute about three-fourths and two-thirds of the total length of chromosome 1. It is assumed that, because of these considerable lengths of the inverted segments, the pairing in the inversion heterozygote should be in part through loop formation and in part through a straight synapsis between the inverted segment and corresponding segment in the standard chromosome, leaving the non-homologous chromosome ends unpaired. An analysis of the observed configurations at meiotic metaphase I indicated the last-mentioned type of pairing in about 60 per cent and the loop type in about 40 per cent of the investigated cells. The induced inversion frequency was less than 0.01 per cent in the present material as compared with a translocation frequency of about 7 per cent for ionizing radiations and 1–2 per cent for chemical mutagens.