Transcriptional activity of an X-borne gene and autosomal control in male fibroblasts. Loci are color coded above panels. (a) Male fibroblast nuclei with transcription from two autosomal GBA alleles (green) and the single X-borne locus (red). (b) Analysis of ATRX by sequential RNA-DNA FISH. Merged panel reveals that the RNA (red) and DNA (green) FISH signals co-localize with no cross-hybridization to the Y paralogue. Nuclei are counterstained with DAPI (blue).