Gene distribution on human chromosomes

The distribution of genes in the human genome is strikingly nonuniform. Gene density is very high in GC (G, guanine; C, cytosine)-rich isochores and very low in GC-poor isochores (isochores are long deoxyribonucleic acid (DNA) regions characterized by a fairly homogeneous GC level). Since GC-rich and GC-poor isochores can be localized on human chromosomes, this ‘chromosomal compositional mapping’ provides information on the distribution of genes on chromosomes. The completion of the human genome sequence and the mapping of isochores on chromosomes have recently confirmed these results.