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تسجيل

Variable base composition in the nuclear genome and the significance of CpG islands

المؤلف:  Strachan, T., & Read, A.

المصدر:  Human molecular genetics

الجزء والصفحة:  5th E, P286

2026-11-02

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The base composition of the nuclear genome averages out at 41.5% GC, significantly less than the 44.4% GC of human mitochondrial DNA. There is considerable variation between chromosomes, from 38.3% GC for chromosome 4 to 47.9% GC for chromosome 19 (see Table 1) and also across the lengths of chromosomes. Chromosomes and chromosomal regions with high and low %GC have, respectively, comparatively high and low gene densities, as described below.

Table1. REFERENCE SEQUENCES AND SOME CHARACTERISTICS OF THE 24 HUMAN CHROMOSOMAL DNA MOLECULES

The proportion of some combinations of nucleotides can vary considerably. Like other vertebrate nuclear genomes, the human nuclear genome has a conspicuous shortage of the CG dinucleotide, often denoted as CpG (to distinguish it from a CG base pair; the p in CpG signifies the intervening phosphate). However, certain small regions of transcriptionally active DNA have the expected CpG density and, significantly, are unmethylated or hypomethylated (CpG islands).