Gigabase

Gigabase is a unit of length used in genomics to describe the size of DNA sequences. One gigabase equals one billion nucleotides. In practice, genome sizes are often reported as haploid base pairs; in that usage, the term may be encountered as Gb (gigabase) or Gbp (gigabase pairs).

Genome sizes vary widely across organisms. The human haploid genome is about 3.0 Gb, corresponding to roughly 3.0 billion bases; the human diploid genome is about 6.0 Gb. Yeast is about 12 Mb (0.012 Gb); maize is around 2.3 Gb. These numbers reflect the amount of sequence a genome project would need to assemble.

Sequencing projects describe outputs in bases and use Gb or Gbp to express coverage and total data. For example, achieving 30x coverage on a human haploid genome (~3 Gb) requires about 90 Gb of sequence data. The unit helps compare projects regardless of whether the genome is small or large.

See also: base pair, genome size, sequencing depth.