Studies on Ascospore Variants of Hypomyces Ipomoeae

SUMMARY

A number of variants which cannot well be explained on the basis of Mendelian segregation of preexisting genes have arisen as the primary growth from single ascospores isolated from both inbred and hybrid perithecia of Hypomyces Ipomoeae.

Hybridization studies have shown the variations, with one possible exception, to have been the result of gene mutation.

The reversion of many of these mutants to the normal type, both in the maturation divisions and in vegetative cells, indicates that the mutations have been of the nature of inactivation or alteration, rather than deletion, of the genes.

The observations strongly suggest that gene mutation is favored in the maturation divisions—particularly in heterozygotes. Effects of the mutations appear in some cases to be carried over into the gametophytic cells of the mutants.

Evidence is presented which indicates that under existing environmental conditions the ascospore variants studied would not be perpetuated in competition with the normal type.