Suitable plasmids are not yet available for use in filamentous fungi, in which stable transformation is dependent on chromosomal integration.DNA-treated cells are usually plated on agar medium that is selective for the desired type of transformant. Most experiments have been concerned with transforming auxotrophic mutants to prototrophy, and in that case, selection of transformants is usually straightforward. Certain wild-type genes capable of complementing auxotrophic mutants have been particularly useful as general-purpose selectable markers and have frequently been incorporated into cloning vectors.sometimes inconvenient consequence of relying on selection against auxotrophy in isolation of transformants is that one must always have the appropriate auxotrophic mutation in the recipient strain. An alternative is to use a dominant mutant gene as the selectable marker. A number of mutations conferring drug resistance, some of bacterial origin, have proved to be suitable for this purpose.