Ove Frydenberg

Some theoretical aspects of the scoring of mutation frequencies after mutagenic treatment of barley seeds

Abstract Recently 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.

The mutation frequency in different spike categories in Barley

Abstract After gamma irradiation of barley seeds, a comparison has been made between the chlorophyll-mutant frequencies in X 1 spikes that had multicellular bud meristems in the seeds at the time of treatment (denoted as pre-formed spikes) and X 1 spikes having no recognizable meristems at the time of treatment (denoted as post-formed spikes). The task was attempted in two ways. First, comparisons were made between plant groups with different numbers of tillers. This analysis revealed no significant differences. Secondly, we compared the mutant frequencies of spikes ranked within each X 1 plant according to their number of flowers, a ranking which was shown to reflect the embryological status of the spike. In this comparison it was found that (a) the frequency of mutated X 1 spikes is larger by a factor of 1·5–2 in pre-formed than in post-formed spikes, (b) the frequency of mutated X 2 plants among all recovered X 2 plants is the same in pre-formed and post-formed spikes, and (c) the frequency of mutant X 3 plants in mutated X 1 -spike progenies (the segregation frequency) is lower by a factor of almost 2 in pre-formed than in post-formed spikes.