The abbreviation DNA (deoxyribonucleic acid) is so well known that it is usually only necessary to spell it out in very technical texts. RNA (ribonucleic acid) is less well known and so, depending on the audience and context, may need to be spelt out at first use.

Bases

Four bases comprise DNA: guanine, cytosine, adenine and thymine. These are abbreviated using the capital letters G, C, A and T. In RNA, the thymine (T) is replaced by uracil (U). Base abbreviations are roman.

Nucleotide sequences

By convention, nucleotide sequences are presented in the 5-prime (5′) to 3-prime (3′) direction. For a single sequence, insert a space after every 5 or 10 symbols:

If it is necessary to indicate the 5′ and 3′ ends, use a hyphen to link these to the sequence:

When aligning homologous sequences, use a font (such as Courier New) that uses the same horizontal space for each letter and punctuation mark, and insert hyphens to maintain the alignment:

Other conventions and abbreviations

• bp – base pairs. Use for DNA sequences with fewer than 1,000 base pairs:

• kbp – kilobase pairs (1,000 base pairs); generally shortened to kilobases (kb):

• Mbp – megabase pairs (1 million base pairs); generally shortened to megabases (Mb). Use for long sequences or to indicate the total number of bases (similarly for gigabase pairs [Gbp] for 1,000 million base pairs):

• cM – centimorgans. Use to describe the genetic distance between 2 loci on a chromosome. Note the capital M.
• DNA and RNA descriptors. Use lower-case letters for descriptors of DNA and RNA: