Relative frequency of single as opposed to compound mutants. Compound mutants harboring 2 paired mutations were almost as frequent (38.3%) as single mutants (49.6%) and were by far more frequent than triple and quadruple (they accounted for 105 of the 138 [76%] compound mutants overall identified). Mutated Ph⁺ populations harboring 3 or 4 mutations in the same BCR-ABL molecule were occasionally detected, but in 1 case only they were found to have achieved clonal dominance over those with 1 or 2 mutations.