The Effect of a Deficiency and a Deletion on Recombination in Chromosome 1BL in Wheat

To test two models of chiasma allocation and the distribution of crossing-over in chromosomes, genetic mapping was performed in normal, deletion and deficiency chromosome arms 1BL of wheat, Triticum aestivum L. Shortening of the chromosome arm, either by a deletion of the proximal half of the arm or by a deficiency of the terminal quarter of the arm's length, significantly reduced the frequency of multiple crossovers but did not affect the distribution of the distal, presumably the first, crossover in the arm. In the deficiency chromosome, the recombination rate in the terminal segment was much higher than that in the same segment of the complete arm. This suggests that recombination frequency is not an inherent characteristic of a segment but depends on the segment's position on the centromere-telomere axis. These observations support the classical model of chiasma distribution along the chromosome based on the point of pairing initiation, chromosome length and the positive chiasma interference. The study also demonstrates that the distribution and frequency of recombination in a chromosome segment can be manipulated. Therefore, even the segments with very low recombination frequencies could be saturated with large numbers of crossover events to produce high-density genetic maps.