In the narrow sense, this term has been applied to the types of molecular change that different mutagens produce in DNA (1). In its widest sense, the term covers all cases in which mutagens vary from each other or from spontaneous mutability in the proportions of the effects they produce, e. g. in the ratios between dominant lethals and translocations, between chromosome breaks in different chromosomes or chromosomal regions, between deletions and gene mutations, between true revertants and suppressors, between forward mutations at different loci or to different alleles at the same locus, or between reverse mutations of genes in the same cell. Mutagen specificity in the narrow sense has been dealt with in previous chapters in relation to the most important mutagens. It is, however, well to bear in mind that there are only very few systems in which specificity at this level can be analysed reliably, and that extrapolation to other systems are fraught with difficulties; we have seen examples of this. In this chapter I am going to deal with specificity in the widest sense. We shall see that only a minority of observed specificities can be attributed unambiguously to reactions between mutagens and DNA, and that often this explanation can be excluded. I shall restrict myself to examples of specificity for gene mutations; more examples will be found in the review by Auerbach and Kilbey (Bibliography).
KeywordsCaffeine Tryptophan Streptomycin Lactose Leucine
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