pergigabase

Pergigabase is a rate unit used in genomics to express the frequency of events per one billion base pairs of DNA. It provides a convenient, scalable way to compare mutation densities, variant discovery yield, sequencing error rates, and other genomic measures across samples, species, and sequencing technologies. The term can be written as gigabase (Gb or Gbp) with or without a space, and is often abbreviated as per Gb or per Gbp in practice.

Common applications include reporting the density of genetic variants—such as germline or somatic mutations—per gigabase, describing sequencing platform error rates per gigabase, and informing power calculations for variant discovery in targeted or whole-genome studies. Pergigabase enables comparisons when genome sizes or targeted region lengths differ among samples.

Calculation and interpretation: if M events are observed in N gigabases of sequence, the density is M divided by N, i.e., events per gigabase. Equivalently, the per-base rate equals (M/N) divided by one billion. For example, sequencing 5 Gb and identifying 2,500 variants yields 500 variants per Gb; for a diploid genome (~6 Gb), this corresponds to about 3,000 variants in total. These figures are influenced by coverage, detectability thresholds, and genome complexity.

Limitations: pergigabase is a normalized metric and not an absolute count. Densities can be affected by uneven coverage, repetitive regions, copy number alterations, and study design. As a result, pergigabase values should be interpreted alongside sequencing depth, method, and region-specific biases.