Complications affecting the Distinction between Mendelian and Maternally Inherited Characters in Neurospora crassa

Abstract

IN the ascomycete, Neurospora crassa, a simple Mendelian character is recognized by 4 : 4 distribution of c and c⁺ expression in spore octets from asci produced by either reciprocal of the cross, c×c⁺. A maternally inherited character^1,2 shows 0 : 8 or 8 : 0 distribution, reappearing only from the reciprocal in which c acts as contributor of the functioning protoperithecia (incipient fruiting bodies formed unisexually). A new character, nova, provides a reminder that phenotypic expressions may actually reflect both forms of inheritance3. Even though it was not expressed by any of the parents, nova appeared regularly from four spores of each octet when the wild strain, Scott A, acted as maternal or protoperithecial parent in crosses (5a, 11–13, Table 2) to sf 51506 18244–7 a, unt 55701 a, thi-1 56501 a and thi-5 50005 5231–7 a, Mendelian marker strains derived from wilds Abbott 4 A and Chilton a^4,5. The character was not expressed in octets from reciprocals of these crosses (Table 1), with the Abbott, Chilton strains as maternal parents. One may therefore assume that expression of nova requires at least two determinants, one maternally inherited, present in Scott protoperithecia, and the other Mendelian, contributed by any one of the Abbott, Chilton strains.