Chromosome size-dependent control of meiotic reciprocal recombination in Saccharomyces cerevisiae: The role of crossover interference

In the yeast Saccharomyces cerevisiae, small chromosomes undergo meiotic re ciprocal recombination (crossing over) at rates (centimorgans per kilobases ) greater than those of large chromosomes, and recombination rates respond directly to changes in the total size of a chromosomal DNA molecule. This p henomenon, termed chromosome size-dependent control of meiotic reciprocal r ecombination, has been suggested to be important for ensuring that homologo us chromosomes cross over during meiosis. The mechanism of this regulation was investigated by analyzing recombination in identical genetic intervals present on different size chromosomes. The results indicate that chromosome size-dependent control is due to different amounts of crossover interferen ce. Large chromosomes have high levels of interference while small chromoso mes have much lower levels of interference. A model for ho-tv crossover int erference directly responds to chromosome size is presented. In addition, c hromosome size-dependent control was shown to lower the frequency of homolo gous chromosomes that failed to undergo crossovers, suggesting that this co ntrol is an integral part of the mechanism for ensuring meiotic crossing ov er between homologous chromosomes.