Reciprocal recombinations at the Charcot-Marie-Tooth disease type 1A (CMT1A) duplication locus in 17p12 and the Smith-Magenis syndrome (SMS) locus in 17p11.2. (a) The non-allelic homologous recombination (NAHR) in which the low-copy repeat (CMT1A-REP) substrates lead to reciprocal CMT1A duplication and HNPP deletion . (b, d, f) Analogous data for the SMS deletion and its predicted reciprocal duplication . (c) The model for the crossover and the predicted junction fragments; (e) the Southern analysis supporting this model. Note that these are the same molecular mechanism (NAHR), but it is shown horizontally (as usually depicted by molecular biologists) in (a) and vertically (as usually depicted by cytogeneticists) in (b). Abbreviations: cen, centromeric; dist, distal; mid, middle; prox, proximal; tel, telomeric.