YEAST COLONY SIZE REFLECTS YAC COPY NUMBER

A novel strategy for separation of co-cloned YACs was developed, For t his, yeast cells were grown under non-selective conditions to allow th e mitotic loss of multiple YACs, Yeast colonies of different size appe ar on 'drop-out' selection plates with small clones consistently conta ining a single-copy YAC. Different auxotrophic marker genes can be use d to separate co-cloned YACs or reduce their copy number, which is ess ential for most YAC-modification procedures.