Studies on the Genetic Multiplicity of a Gene in Yeast Cells II. Effects of Ultraviolet Light

In the hope of obtaining the genetic multiplicity of the ad gene in yeast cells, the relationship between UV dosage and forward mutation frequency was studies. It was observed that UV induced two types of mutation, fractional- and whole-colony, at the ad locus. The ratio of the whole-colony to the fractional-colony increased with UV dose. By theoretical treatment, it was deduced that the fractional-colony mutation was induced by a single-hit and the whole-colony mutation by two single-hit events in sequence, this sequence seeming to have a high probability to occur. These results support the conclusion that the genetic multiplicity of the gene is two, probably corresponding to the individual strands of double-stranded DNA.