This lungfish, known as 'living fossil', has largest-ever genome decoded, 30 times bigger than ours

Researchers have decoded the largest animal genome, and it doesn't belong to giants like whales or elephants, but to a humble but strange-looking fish. The lungfish genome was found to be 30 times the size of the human genome.

The sequencing was carried out by an international team of researchers led by Konstanz evolutionary biologist Axel Meyer and Würzburg biochemist Manfred Schartl.

Why is lungfish so special? The living fossil

The lungfish is called so because it actually has lungs, unlike most other fish species, a characteristic it retained from its ancestors who could move and breathe on land. The freshwater fish come in mainly three varieties: South American, African and Australian.

Lungfish are known as 'living fossils' because they retain some of the traits of their ancient ancestors from hundreds of millennia ago.

The Australian lungfish retainthe limb-like structures that once enabled their ancestors to move on land. These are absent in their African and South American relatives, having evolved into fin-like structures for swimming.

Lungfishshare ancestors with all other four-limbed vertebrates known as tetrapods.

Why does lungfish have such big genome?

According to a press release from the researchers, the South American lungfish breaks all records for size, with its DNA having more than90 gigabases. One gigabase is90 billion bases.

Earlier, the record was held by its cousin, the Australian lungfish, which had around half that number. "18 of the 19 chromosomes of the South American lungfish are each individually larger than the entire human genome with its almost 3 billion bases,” said Meyer, an evolutionary biologist at the University of Konstanz in Germany.

The cause for such enlarged DNA is 'autonomous transposons'.Autonomous transposons are DNA sequences that “replicate” and then change their position in the genome, which in turn causes the genome to grow, said the study, with the South American lungfish showing the fastest rate of such expansion.

The researchers estimated that the lungfish genome grew by the size of the entire human genome every million years.

“And it continues to grow. We have found evidence that the transposons responsible are still active,” said Meyer.

In spite of the expansion, the lungfish genome is remarkably stable, similar to their ancestral tetrapods, said a release on the study.

(With inputs from agencies)