A novel mutation that affects utilization of galactose in Saccharomyces cerevisiae II. A partial aneuploid for chromosome II isolated as a revertant of the mutant.

An aneuploid strain of Saccharomyces cerevisiae was isolated from a haploid strain with gal11, mutation of which would presumably occur through mitotic nondisjunction. The strain carries an extra copy of chromosome II deleted for a distal part of its left arm covering ISL1. The partial chromosome is stably inherited in repeated meioses. The aneuploid strain is also mitotically stable and remains disomic for more than 99.5% of the time. The transfer-hybridization experiment with radioactively labelled λ phage DNA containing yeast GAL genes as a probe indicated that the aneuploid strain contains two copies of those genes.