REGIONAL BIVALENT-UNIVALENT PAIRING VERSUS TRIVALENT PAIRING OF A TRISOMIC CHROMOSOME IN SACCHAROMYCES-CEREVISIAE

In meiosis I, homologous chromosomes pair, recombine and segregate to opposite poles. These events and subsequent meiosis II ensure that eac h of the four meiotic products has one complete set of chromosomes. In this study, the meiotic pairing and segregation of a trisomic chromos ome in a diploid (2n + 1) yeast strain was examined. We find that triv alent pairing and segregation is the favored arrangement. However, ins ertions near the centromere in one of the trisomic chromosomes leads t o preferential pairing and segregation of the ''like'' centromeres of the remaining two chromosomes, suggesting that bivalent-univalent pair ing and segregation is favored for this region.