EXCHANGES ARE NOT EQUALLY ABLE TO ENHANCE MEIOTIC CHROMOSOME SEGREGATION IN YEAST

Homologous chromosomes pair, and then migrate to opposite poles of the spindle at meiosis I. In most eukaryotic organisms, reciprocal recomb inations (crossovers) between the homologs are critical to the success of this process. Individuals with defects in meiotic recombination ty pically produce high levels of aneuploid gametes and exhibit low ferti lity or are sterile. The experiments described here were designed to t est whether different crossovers are equally able to contribute to the fidelity of meiotic chromosome segregation in yeast. These experiment s were performed with model chromosomes with which it was possible to control and measure the distributions of meiotic crossovers in wild-ty pe cells. Physical and genetic approaches were used to map crossover p ositions on model chromosomes and to correlate crossover position with meiotic segregation behavior. The results show that crossovers at dif ferent chromosomal positions have different abilities to enhance the f idelity of meiotic segregation.