Practice question

Complementation groups represent functional genetic units each group consisting of mutants failing to complement each other and therefore allelic and affecting same cistron. In screens for same phenotype multiple independent mutations may fall into same group because same enzyme affected while mutations in other enzymes fall into other groups. Number of distinct groups thus equals number of different genes whose loss can produce phenotype. Six mutants partitioning into three groups therefore imply three separate loci required for normal process each group corresponding to one gene in pathway.