QUANTITATIVE AND QUALITATIVE COMPARISON OF SPONTANEOUS AND CHEMICAL-INDUCED SPECIFIC-LOCUS MUTATION IN THE AD-3 REGION OF HETEROKARYON-12 OF NEUROSPORA-CRASSA
Fj. Deserres et al., QUANTITATIVE AND QUALITATIVE COMPARISON OF SPONTANEOUS AND CHEMICAL-INDUCED SPECIFIC-LOCUS MUTATION IN THE AD-3 REGION OF HETEROKARYON-12 OF NEUROSPORA-CRASSA, Mutation research, 375(1), 1997, pp. 53-72
The data from forward-mutation experiments to obtain specific-locus mu
tations at two closely linked loci in the adenine-3 (ad-3) region of h
eterokaryon 12 (H-12) of Neurospora crassa have been tabulated to dete
rmine the relative frequencies and mutational spectra of ad-3 mutants
occurring spontaneously and those induced by 22 different chemical tre
atments. Previous studies have demonstrated that specific-locus mutati
ons at these two loci result from 5 major genotypic classes, namely tw
o classes of gene/point mutations (ad-3A(R) and ad-3B(R)), and 3 class
es of multilocus deletion mutations ([ad-3A](IR), [ad-3B](IR) and [ad-
3A ad-3B](IR)). In addition, prior studies have demonstrated that some
chemical mutagens induced ad-3 mutants exclusively, or almost exclusi
vely, by gene/point mutation and other chemical mutagens by gene/point
mutation and multilocus deletion mutation. In the latter cases, there
was wide variation in the percentages of ad-3 mutants in these 5 majo
r genotypic classes. Two comparative methods of analysis that also wer
e used to compare spontaneous and chemical-induced ad-3 mutational spe
ctra included chi(2)-tests on the numbers of ad-3 mutants resulting in
the following two sets of ratios: (1) gene/point mutations and multil
ocus deletion mutations; and (2) complementing and non-complementing a
d-3B(R) mutants. Combination of the p-values from chi(2)-tests for the
se two methods of comparison demonstrated that all 22 chemicals induce
a spectrum of ad-3 mutants that is qualitatively different from that
occurring spontaneously. In addition, these same two methods of compar
ison have been used to compare the mutagenic effects of each of the 22
chemical treatments with each other. Combination of the data from the
se two methods of comparison has demonstrated that 93.1% (215/231) of
the pairwise combinations of these 22 chemicals were different from ea
ch other. The implication of these experimental data on the induction
of specific-locus mutations in somatic cells of Neurospora for genetic
risk assessment exercises is discussed.