A significant advantage ofPichia pastorisas an experimental system is the ability to bring to bear readily both classical and molecular genetic approaches to a research problem. Although the recent advent of yeast molecular genetics has introduced new and exciting capabilities, classical genetics remains the approach of choice in many instances. These include: the generation of mutations in previously unidentified genes (mutagenesis); the removal of unwanted secondary mutations (backcrossing); the assignment of mutations to specific genes (complementation analysis); and the construction of strains with new combinations of mutant alleles. In this chapter, these and other methods for genetic manipulation ofP. pastorisare described.
