TETRAPLOID STRAINS OF SACCHAROMYCES CEREVISIAE THAT ARE TRISOMIC FOR CHROMOSOME III

Michael I. Riley ¹ and T. R. Manney ¹

¹ Department of Physics, Kansas State University, Manhattan, Kansas 66506

Meiotic segregation of several genes has been studied in tetraploid strains that are trisomic for chromosome III. The segregation data were compared to a computer simulation that assumes trivalent pairing of homologues involved in exchanges, followed by nonpreferential segregation. Trivalent pairing was characterized by higher frequencies of exchange as compared to bivalent pairing, and by the presence of spores resulting from at least double crossovers involving all three homologues. Trivalent segregation was characterized by a unique recombinant class. The strong interference normally exhibited in diploid meiotic recombination was not evident from the frequency of double crossovers in these strains.