The Effects of Supplementation and Plating Densities on Apparently Aberrant Meiotic and Mitotic Segregation in Aspergillus Rugulosus.

I T was recently observed that when random ascospores from hybrid cleistothecia were analyzed, markers conferring nutritional competence were recovered in a significantly higher proportion than would be expected on a random basis (COY and TUVESON 1964a). In this same investigation, non-nutritional markers such as those controlling conidiation and color of conidia were recovered with the expected frequencies. The present paper presents evidence which suggests that the distorted ratios for nutritional markers are not the result of aberrant mechanism (s) of segregation or the formation of “partial hybrid” cleistothecia (PONTECORVO, R PER, HEMMONS, MACDONALD and BUFTON 1953; COY and TUVESON 1964b), but rather may be explained on the basis of a reduced “fitness” of specific mutants. Further, evidence is presented which suggests that mutant alleles which are not recovered at random among random ascospores will not be recovered among somatic segregants.