Except for when individuals have variations in the pericentric heterochromatic chromosomal regions (including acrocentric short arms), it is not possible to distinguish between homologous chromosomes at a single-cell level. Due to this limitation, various questions of scientific and diagnostic relevance have been off-limits. Based on copy number variations (CNV) spanning up to several megabasepairs of DNA, we developed a molecular cytogenetic approach for the interindividual differentiation of homologous chromosomes, the so-called parental origin determination fluorescence in situ hybridization (pod-FISH) technique. To perform this technique, all human chromosomes are covered with CNV-spanning BAC probes in one- to five-color chromosome-specific pod-FISH sets. This new approach to studying the parental origin of individual human chromosomes at a single-cell level has opened new horizons for diagnostics and basic research.
