Some Theoretical Aspects of the Scoring of Mutation Frequencies after Mutagenic Treatment of Barley Seeds

Recently Gaul(3,4,6) has discussed the various methods of scoring recessive mutants after seed treatment in barley. According to this author certain advantages should be gained by recording the X2 mutant frequency among all X2 plants raised in these experiments. Investigating in the properties of the “X2-mutant-frequency” measure, a mathematical model is presented in the present paper.

When a few well defined and unavoidable assumptions are accepted, it is demonstrated that the X2 mutant frequency for all practical purposes is proportional to the initial mutation frequency as has been claimed by Gaul. The nature of the proportionality factor between the initial mutation frequency and the X2 mutant frequency is discussed in some details.

It is shown that this factor is not always identical with the segregation frequency of the same class of mutants from heterozygous plants. A formula is derived for estimating the standard deviation of the X2 mutant frequency by means of an enumeration of the mutant clusters recovered among the X2 plants.

The practical use of this formula is demonstrated by applying it to material obtained after irradiation of dormant barley seeds with two doses of γ-rays.