Meiotic segregation of normal and deletion chromosomes in Saccharomyces cerevisiae

We explored the behavior of meiotic chromosomes in Saccharomyces cerevisiae by examining the effects of chromosomal rearrangements on recombination and disjunction. Chromosome III derivatives in which the entire left arm or the entire right arm was deleted (telocentric) segregated with fidelity from a normal chromosome III. Recombination between either of these two deletion chromosomes and the intact chromosome also appeared normal. In a strain containing a right arm telocentric, a left arm telocentric and one normal chromosome both telocentrics disjoined from the normal chromosome. Homology on one arm was sufficient for proper recombination and segregation of these chromosomes. In strains containing two normal chromosomes and one telocentric chromosome the two normal chromosomes preferentially disjoined. In a few cases however, the two normal chromosomes cosegregated. Recombination between the two normal chromosomes or between one normal chromosome and the deletion chromosome increased the probability that they would disjoin, although cosegregation of recombinants was observed. A chromosome III derivative which contained a large centromeric deletion and an insertion of the centromere from chromosome V into a nonhomologous position segregated with fidelity from a normal chromosome III. These studies demonstrate that it is not pairing of the centromeres, but pairing and recombination along the arms of the homologs that directs meiotic chromosome disjunction.