ESTIMATION OF MITOTIC STABILITY IN CONIDIAL FUNGI - A THEORETICAL FRAMEWORK

Mitotic stability refers to the probability that genetic elements are transmitted to both daughters during mitosis. This is of practical imp ortance in molecular genetics because autonomous cloning vectors shoul d be transmitted at high frequency during mitosis. In filamentous coen cytic fungi it is difficult to quantify mitotic stability because a fl uctuation test is not feasible. We show how to get around this problem by formulating a general model of the transmission of nuclear genetic elements through the course of conidiogenesis. We derive formulas by two different methods for the expected proportion of conidiospores tha t retain the element as a function of its mitotic stability and the nu mber of generations of spore production. An important by-product yield s the exact probability distributions for the number of conidiospores retaining elements at each stage of conidiophore development. We outli ne, and illustrate through specific numerical examples, how to use the se formulas to estimate mitotic stability. Although we use Aspergillus nidulans as our biological paradigm, the same general framework can b e extended to other fungal species, and possibly to less closely relat ed systems as well.