Abstract: Methods and apparatuses for selecting and arranging clinically relevant chromosomal loci allow an exemplary diagnostic array to simultaneously test for numerous genetic alterations that occur in many different parts of the human genome. Clinically irrelevant or ineffective loci are eliminated. One implementation increases reliability and accuracy by dividing the base-pair sequence of each chromosomal locus into segments and then assigning nucleic acid clones for comparative genomic hybridization to each different segment. The segments may overlap for increased resolution and control. Clones representing segments that are adjacent on a native chromosome are placed in non-adjacent target areas of the array to avoid interfering hybridization reactions. Arrangement motifs within an array may be redundantly repeated for high availability and increased reliability and accuracy of results. Techniques, hardware, software, logic engines, loci collections, and diagnostic arrays are described.