Xist RNA (labeled by a red rhodamine dye) covers one of the two copies of the X chromosome. The expression of Xist will lead to the chromosome’s inactivation. The image is from an RNA fluorescent in situ hybridization (FISH) experiment performed on a metaphase chromosome spread taken from a female fibroblast cell line.

[J. T. Lee et al., “Lessons from X-chromosome inactivation: long ncRNA as guides and tethers to the epigenome,” Genes Dev., 23 (16), 2009, 1831–1842, Fig. 2. © Cold Spring Harbor Laboratory Press. Photography by Jeannie Lee.]