The interpretation of complementation data

Abstract

The evidence for complementation maps being linear is examined by analysis of all known complementation maps in micro-organisms, and by constructing maps from mutants randomly sampled from amongst those at the leu-2 locus in Neurospora with known complementing properties. Eleven loci out of thirty-five examined in six micro-organisms have non-linear complementation maps. Two linear maps, his-3 and ad-3b (having 25 and 35 complementation groups respectively) have a sufficiently large number of groups for it to be likely that if they do not remain linear on testing further mutants, they will at least have a lower frequency of mutants exceptional to linearity than known non-linear loci. On the basis of maps made from mutants sampled from the leu-2 data, it seemed unlikely that non-linearity would be observed with less than 24 complementing mutants or 13 complementing groups in the sample, and therefore many loci with linear maps are likely to be found to have non-linear maps when larger samples of mutants are tested. This conclusion is important in attempting to correlate the structure of complementation maps with recombination maps and with functional data concerning enzyme activities.The relationship between the number of complementing mutants, number of groups and number of units at the leu-2 locus is described and a statistical method of determining the total number of groups at a locus is discussed.Known complex complementation maps have been replotted according to consistent rules, and are illustrated in a shorthand form. The form of the complex maps is discussed in relation to current hypotheses concerning the interpretation of complementation maps. In particular an interpretation of the ‘circular’ leu-2 map is given in terms of the theory of complementation proposed by Crick & Orgel (1964).