A number of studies have provided convincing evidence that co-expressed genes are often found in clusters in the yeast, fly, worm or human genomes. In the December 12
Analysis of available EST databases identified 4,271 testes-expressed genes, of which 1,661 appear to be testes-specific. Mapping each EST to the fly genome revealed that about one third of testes-specific genes are clustered. Many of these clusters (45%) contain four or more genes. A notable exception was chromosome X, which showed little clustering of testes-specific genes and smaller cluster sizes. Additional EST-based analysis also showed clusters of head-specific genes and embryonic genes.
Much remains to be discovered about the role of chromatin structure in the transcriptional regulation of genome clusters.