Abstract
Evidence of spontaneous n+1 aneuploidy has been obtained by trisomic segregation analysis of four independently maintained stocks of Saccharomyces cerevisiae defective in saturated fatty acid synthesis (fas1). In all cases tested, only the chromosome bearing the mutant fatty acid locus was disomic. Tetrad analysis of trisomic hybrids enabled the identification of chromosome XI as the one bearing the fatty acid locus and the assignment of fragment 5 to chromosome XI. Statistical analysis of tetrad frequencies generated by markers in triplex configuration provided information on the meiotic configuration of pairing of the three homologous chromosomes. The possible relationship between defective nuclear membranes and the disjunction of chromosomes in fas1 strains is discussed.