GCContent

GC content is the proportion of guanine and cytosine bases in a DNA or RNA sequence, typically expressed as a percentage of the total nucleotides. Because G pairs with C via three hydrogen bonds, sequences with high GC content are more thermally stable than AT-rich sequences.

Calculation: GC content = (G + C) / (A + T + G + C) × 100. It can be reported for the whole sequence or calculated in sliding windows (for example, 100 base pairs) to reveal regional variation.

Baseline values: Across life, GC content varies widely. Bacteria often range 25–75%, with many bacteria around 40–60%. Eukaryotes typically around 40–60%, though plants and some amphibians have high GC content. The human genome averages about 41%, while regions called isochores show long-range GC variation.

Biological and technical implications: GC content affects DNA stability, melting temperature, codon usage, and gene expression. Very high or low GC regions can pose challenges for PCR amplification, sequencing, and cloning due to polymerase bias or secondary structures.

Applications and measurement: GC content is used in genome annotation, comparative genomics, primer design, and quality control of sequencing data. It is computed by bioinformatics tools from genome assemblies or reads; GC% is reported for whole genomes, chromosomes, genes, or sliding windows.