Figure 1.

Flow chart of wet bench procedures for YAC → cosmid and BAC → cosmid MCD mapping. The main difference is that, while BAC DNA can readily be purified from bacterial chromosomal DNA, there is no good preparative method to separate YAC DNA from yeast chromosomal DNA. In the YAC case, the few percent of the cosmids that are derived from the YAC are identified by a hybridization-based colony-screening protocol. With BAC-derived cosmids, this step is unnecessary because the mapping software can readily eliminate the small number of cosmids that do not originate from the BAC.