Figure 2.
Altered chromosome transmission events in SGA. (A) Gene conversion. A diploid in meiosis can convert either of the two his3Δ1 alleles (shaded block arrow) prior to meiosis I. The vast majority of spores selected on SC–histidine containing canavanine (SC–his + CAN) after meiosis are MATa PMFA1-HIS3 his3Δ1 can1 (solid block arrow, left side). Gene conversion followed by appropriate meiotic segregation can generate rare MATα HIS3 can1 (arrow, right side). The MATα cells are surrounded by MATa cells and mate, producing diploids that escape the haploid selection and confound the SGA. (B) Flow cytometry of false negative colonies. Fifteen colonies from a bni1 × bni1 cross that mated with a MATα tester were grown to midlog, prepared for flow cytometry, and compared to BY4741. Three classes were recovered. Class 1 had an approximate haploid content of DNA, while classes 2 and 3 appeared aneuploid.