Cytology and genetics of two abnormal ascus mutants of Neurospora.

Abstract

A new mutant of Neurospora, called scruffy, acts as a zygote recessive in determining asci with altered arrangements, and sometimes altered numbers, of ascospores. Cytological observations show that the morphological deviations seen in mature asci are preceded by differences in orientation of spindles for the nuclear divisions occurring within the developing asci, and that spindle disposition is influenced by the size and shape of the cells. The ultimate effects on spore shape and number appear to result from a disruption of the interaction between cell wall and elongating spindles that in N. crassa determines the uniseriate arrangement of eight spores. A nonallelic mutant, scumbo, also acts as a zygote recessive in effecting deviant ascus morphology. A demonstration of complementation between nonallelic mutants affecting ascus morphology provides additional evidence referring to zygotic control of the development of the ascus in Neurospora.