Fig. 1.

Two systems for the detection of mitotic recombination and chromosome loss in diploid yeast cells. (A) One commonly used system for detection of mitotic recombination events uses a diploid that is heterozygous for mutations in the can1 and hom3 loci. The starting diploid strain is Can^S and Met⁺. The depicted strain is also homozygous for the ade2-1 mutation that results in cells that are Ade⁻ and form red colonies. Cells are transferred to plates containing Can, and any Can^R derivatives are tested for their ability to grow in the absence of methionine. Met⁻ cells represent chromosome loss events, and Met⁺ cells are assumed to represent mitotic cross-overs. Note that the CAN1/CAN1 product cannot be selected by this system. (B) Selection of both products of an RCO in the diploid MAB6. The starting diploid is phenotypically Can^S Gen^R Hyg^R His⁺ Leu⁺ Ade^+/− and forms white colonies. An RCO between the centromere and the CAN1 locus will result in a Can^R colony with one red and one white sector, resulting from the growth of two Can^R cells, one with the genotype can-100/can1-100 and one with the genotype SUP4-o/SUP4-o. Hyg^S, hygromycin-sensitive; Gen^S, geneticin-sensitive.