Classes of mutants identified by the number of WD40 repeat units. A/The WD domain of the het-r gene of a selection of mutants from the RV collection were PCR amplified and separated on an 0.8% agarose gel (molecular marker: 1 kb ladder). The sizes of the amplicons are compared to the natural inactive (het-r) and active (het-R) alleles. B/Three classes of mutants are defined according to the size of the WD repeat domain of the het-r or the het-e gene: the deletion mutants (dWD), the gain of WD40 repeat mutants (gWD) and the mutants with the same number of WD40 repeats as the initial allele (snWD). Subclasses of mutants are defined according to the number of WD40 repeat units deleted (-) or gained (+) compared to the initial allele. The percentage of the total number of mutants comprised in each subclass is represented.