Differential accessibility and equivalent accessibility patterns between metaphase chromosome homologs detected by single copy probes. A. Human chromosomes hybridized with single copy FISH probes developed from CACNA1B (2.23 kb), HERC2 (1.81 kb), and PMP22: IVS3 (2.32 kb) (left to right) show differential hybridization between homologs. Arrows indicate the homolog with less fluorescence (or less accessibility). B. Examples of human cells with single copy FISH probes developed from within CCNB1 (2.47 kb), C9orf66 (2.08 kb), and BCR (3.4 kb) (left to right) that show similar fluorescence intensities (or equivalent accessibility) between homologous regions. Chromosomes were counterstained with DAPI (converted to gray scale in image) and probes were labelled with digoxigenin d-UTP and detected with Cy3 digoxin antibody.