A) Schematic representation of the centromeric regions of chromosomes 1, 5 and 19. The three chromosomes share an alphoid array where the active centromere normally forms: D1Z7, D5Z2, and D19Z3 (15). As shown by Finelli et al (14), D1Z7 is embedded within D1Z5. Chromosomes 5 and 19 share a second alphoid array: D5Z1 and D19Z1. In situ hybridization with both pZ5.1 DNA (green signal) and BAC RP11-483B6 DNA (red signal) as probes on chromosomes in prometaphase (B, D) and nuclei (C).