On the island of New Caledonia, a simple, unassuming species of fern has been identified as having the longest genome of any living organism known.
It is 50 times longer than a human’s, 7% longer than the previous world record-holding species for longest genome, and 20% longer than the record-holding animal.
Compared to 23 pairs of chromosomes in every human cell, the tiny fern contains 416—and if unraveled, would climb higher than Big Ben in London’s Westminster.
Questions abound, as does admiration for the majesty and mysteries of biological life.
“Compared to other organisms, plants are incredibly diverse when viewed at the DNA level, and that should make us pause to think about their intrinsic value in the wider picture of global biodiversity,” said Dr. Ilia Leitch, Senior Research Leader at the Royal Botanical Gardens, Kew.
“This discovery also raises many new and exciting questions about the upper limits of what is biologically possible, and we hope to solve these mysteries one day.”
Tmesipteris oblanceolata is a species of New Caledonian fork fern that grows on the ground or out of rotting tree trunks. A team from Kew and the Institut Botànic de Barcelona traveled to New Caledoina’s largest island of Grand Terre to collect this species for study.
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20,000 species from the Tree of Life have had their genomes completely sequenced, and this literature has shown that having a complex genetic code isn’t always an advantage.
Larger genomes require more resources for DNA replication, repair, and transcription, while a larger DNA sequence needs a larger nucleus, and therefore a larger cell, to house it.
Dr. Leitch told Reuters that “perhaps unsurprisingly, species with larger genomes are at greater risk of extinction,” for a similar reason, one might imagine, that simpler machines with fewer moving parts tend to last longer than complicated and sophisticated machines with many; a Honda Civic will run longer than a Lamborghini Aventador.
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The previous record holder for the longest genome was the Japanese flowering plant species Paris japonica while the longest genome known from the animal kingdom is the African marbled lungfish, (Protopterus aethiopicus).
The smallest genome is the fungus species Encephalitozoon intestinalis, with 2.6 megabase pairs. For context, the New Caledonian fork fern contains 168 gigabase pairs. An appropriate comparison would be to compare the file size of the original Tetris game to that of a modern open-world role-playing game like The Witcher or World of Warcraft.
For those with greater interest in DNA, Dr. Leitch and her colleagues from Kew and IBB published a paper on the fork fern, writing that genome size variation and its disconnect from species complexity, “is known as the ‘C-value paradox’ or ‘C-value enigma,'” and has intrigued biologists for over half a century.
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“Rapid advances in DNA sequencing are now providing compelling evidence showing that variation in DNA amount arises predominantly from differences in the frequency of polyploidy, abundance of non-coding repetitive DNA, and the dynamics of the processes that amplify, erode, and delete DNA,” they write in their introduction.
However with only 20,000 species that have had their genomes sequenced, the authors doubt that science has uncovered the full extent of genome size diversity.
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