How to test for complementation between mutant strains

Dodge (1942, Dodge et al. 1945) provided the first example of complementation in N. tetrasperma. Beadle and Coonradt (1944) explored complementation in heterokaryotic strains with multiple components, in hope of determining degrees of dominance. With the advent of efficient methods for selecting auxotrophic mutations, series of mutants with the same requirement were tested for allelism by complementation tests which used heterokaryons to place them in complementation groups that corresponded to different loci (e.g., de Serres 1956, Webber and Case 1960). A similar analysis has used heterokaryon formation to place new morphological mutants in >100 different complementation groups (Seiler and Plamann 2003).