Largest animal genome

The largest genome (i.e., total amount of DNA in the nucleus of a cell) for an animal assessed to date using best-practice methods is 129.9 billion base pairs (Gbp, or gigabase pairs), for the marbled lungfish (Protopterus aethiopicus) of Africa as documented in the Journal of Experimental Zoology by Dr Keith Thomson in June 1972. This fish boasts over 40 times more genetic material than that found in the nuclei of human cells (3.2 Gbp).

To determine genome size, the most common technique that scientists employ is “flow cytometry”. This involves first isolating nuclei and staining them with a fluorescent dye that binds quantitatively to the amount of DNA present in each nucleus. The suspended nuclei are then loaded onto the flow cytometer and as they pass through a laser beam the amount of fluorescent light is measured (the bigger the genome, the more fluorescent light is detected by the flow cytometer). As well as the number of base pairs, genome size can also be expressed as a weight in picograms (one-trillionth of a gram): the total DNA of the marbled lungfish weighs in at 132.8 picograms.

If fully unravelled, the DNA from a cell of the marbled lungfish would span in excess of 85 m (279 ft) – about 1.5 times the height of the Leaning Tower of Pisa; a human’s total DNA in a cell, by comparison, would “only” stretch about 2 m (6 ft 6 in).

The largest animal genome to have been sequenced and assembled is that of the related Australian lungfish (Neoceratodus forsteri): 43 Gbp of its genome has been reconstructed according to a study in Nature in 2021; this surpassed the previous 32 Gbp sequenced for the axolotl salamander (Ambystoma mexicanum) as of 2018.

The largest genome for a plant – as well as for any organism overall using flow cytometry – is 160.45 Gbp – or 164 picograms – for the Tmesipteris oblanceolata fork fern. It is native to tropical forests in the French overseas territory of New Caledonia and other nearby islands, such as Vanuatu, in the south-west Pacific Ocean. The findings were published in the journal iScience on 31 May 2024.