Ciliates employ massive chromatid breakage and de novo telomere formation during generation of the somatic macronucleus. Positions flanking the 81-MAC locus are reproducibly cut. But those flanking the Common Region are proposed to often escape cutting, generating three nested macronuclear chromosomes, two retaining "arms" still appended to the Common Region. Arm-distal positions must differ (in cis) from the Common Region flanks.