Meiotic crossing-over in the regions of homology between homologous chromosomes V.

Homologous chromosomes V of Saccharomyces cerevisiae and S. carlsbergensis virtually do not recombine in meiosis. Artificially created short regions of homology were found to induce meiotic crossing-over if they contained sequences located upstream of the S. carlsbergensis ILVI gene. Heterozygous restriction site markers were introduced within the 1.1 kb region of homology to monitor conversion events associated with the crossovers. In the presence of five heterozygosities, 85% of crossovers showed associated conversion. Crossovers with no detected conversion were found in the two largest (0.34 and 0.29 kb) intervals, into which the 1.1 kb region was divided by the introduction of the five markers, whereas the shortest conversion tracts observed did not exceed 0.26 kb. Several lines of evidence suggest that each crossover required a formation of heteroduplex DNA with the considerable minimal length of approximately 200-260 bp. Copyright 2001 John Wiley & Sons, Ltd.