DNA-RNA immunoFISH analyses of GFLC fraction 2 from ΔLCR/WT heterozygous fetal liver cells. 2 Z-sections, which contain allelic signals derived from the same cell, are shown (panels A and B, and panels C and D). Cells were stained by DAPI (A,C), anti–H3 K79 dimethylation (blue in panels B and D). The cells are also hybridized with a β-globin BAC (green in panels B and D) and the second intron of the adult β-globin (red in panels B and D) probes for detecting the loci and β-globin primary transcripts, respectively. Merged images of the alleles (green), primary transcripts (red), and H3 K79 dimethylation foci (blue) are shown. A part of each color channel from merged images in panels B and D is magnified and shown in panels E and F, respectively. Both color (top row) and gray (bottom) images are shown. The WT (green; panels B and E) and ΔLCR (green; panels D and F) alleles in heterozygous cells were identified based on primary transcript signals. Frequencies of colocalization of the WT and ΔLCR alleles are plotted (G). Each bar represents the average of 2 separate data sets (N = 20 + 26 [WT]; N = 28 + 29 [ΔLCR]). Error bars represent SD. Scale bars equal 10 μm. Image acquisition information can be found in Document S1.