Genetic analysis of eight-spored asci produced by gene E in Neurospora tetrasperma.

NLIKE the better-known eight-spored species of Neurospora, N . tetrasperma usually produces asci with only four ascospores; each ascospore contains nuclei derived from two of the four meiotic products and is usually heterokaryotic for the mating type alleles. DODGE (1939) showed that eight-spored asci also occurred in N . tetrasperma, in crosses heterozygous for the pleiotropic gene E. Such crosses often showed a high frequency of aborted asci but when fertile yielded varying proportions of both eight-spored and four-spored asci in the same perithecia. Crosses homozygous for E were never fertile. The vegetative cycle was also affected, for ascospores containing the E allele usually died as germlings, although their survival frequency could be somewhat increased by enriched media. The cytology of asci heterozygous for E has been previously investigated (DODGE, SINGLETON and ROLNICK 1950; SINGLETON, cited by BRAVER 1952) , but these authors, as well as HOWE and HAYSMAN (1966), made only limited genetic analyses. Both the interest and the potential usefulness of E made it desirable to gain a further understanding of the nature of this allele. The present analysis of asci heterozygous for E aims to interpret the various segregation patterns and to correlate these patterns with earlier cytological observations. Our efforts were greatly facilitated by using one of DODGE'S E strains which was found to have lost much of the lethality described above, such that ascus abortion was markedly reduced, and all eight ascospores from the asci usually survived the germling stage.