The South American lungfish most likely has numerous “junk” DNA
Katherine Seghers/Louisiana State College
There’s a new report for the biggest genome to be sequenced, set at an enormous 90 billion letters of DNA. It belongs to the South American lungfish.
“It was a technical challenge, of course, to do this,” says Axel Meyer on the College of Konstanz in Germany. “It is the largest of all animal genomes.”
Every cell within the South American lungfish (Lepidosiren paradoxa) has two copies of the genome, comprising 180 gigabases (Gb) of DNA in complete that might stretch for 55 metres if organized in a line. That’s 30 instances greater than the 6 Gb of DNA in every human cell.
The South American lungfish has 19 chromosomes, 18 of that are every bigger than a single copy of the human genome, says Meyer.
His crew additionally sequenced the 40 Gb of a single copy of the genome of the African lungfish (Protopterus annectens), which means the researchers have now sequenced all six lungfish species discovered globally, which all have abnormally massive genomes.
“It’s a real enigma how these fish are able to tolerate such a large genome,” says Meyer. The nucleus inside every cell must be very massive to slot in a lot DNA, he says, which suggests every cell is bigger than regular. Replicating a lot DNA additionally takes numerous vitality every time cells divide.
There isn’t a proof that every one this additional DNA does something helpful. Fairly, it seems to be a results of “genetic parasites” making countless copies of themselves. It’s most likely largely junk, says Meyer.
His crew discovered that mechanisms that different organisms use to curtail the unfold of genetic parasites appear to be broken or lacking in all of the lungfish species. In consequence, the genome of the South American lungfish has been rising by 3.7 Gb – greater than a single copy of the human genome – each 10 million years.
The explanation for sequencing all of the lungfish species is to get a greater thought of what their shared ancestor was like. That ancestor was an in depth relative of the lungfish that advanced into the primary four-legged land animal.
“They are our closest relative among the fishes,” says Meyer. As their identify implies, lungfish breathe air and drown with out it.
They will additionally stay for greater than 100 years and regenerate their fins and tails, he says. Meyer’s crew hopes to learn the way they obtain this.
Some plant genomes are even bigger than that of the South American lungfish. A small fern discovered on just a few Pacific islands is believed to have 321 Gb of DNA in every cell, however there aren’t any plans to attempt to sequence it.
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