Abstract
Apparent non-Mendelian segregation encountered in a cross between adenine independent and adenine dependent haploid strains is explicable by postulating a multiple genetic control of adenine formation. One of these genes, which arose by spontaneous mutation in a originally pink adenine dependent culture, is presumed to block adenine synthesis prior to those already present in the stock. The postulated ad3 mutation is not linked with the other adenine genes, which, when mutant, cause color production, but it is epistatic to them.
