Team Factend
In a groundbreaking scientific achievement, researchers have sequenced the largest animal genome known to date, belonging to the South American lungfish (Lepidosiren paradoxa). With a genome size 30 times greater than that of humans, this remarkable discovery has sparked interest across the scientific community, revealing intriguing insights into the evolutionary journey of this prehistoric species.
The South American lungfish is an ancient, air-breathing fish with limb-like fins, capable of “hopping” onto land from water. Often referred to as a “living fossil,” this species has survived for hundreds of millions of years and is considered a close relative of the first tetrapods—the ancestors of all vertebrates. These ancestors made their historic transition from water to land approximately 370 million years ago during the Devonian period, making lungfish essential to understanding evolutionary biology.
A Genome of Unprecedented Size
The lungfish genome, sequenced and published in Nature on August 14, 2024, is composed of an astounding 91 billion base pairs of DNA, a size previously unimaginable in the animal kingdom. To put this into perspective, this genome could fill the equivalent of 100,000 books, with only 20,000 of its genes encoding for proteins. The remaining majority, over 90%, consists of transposable elements (TEs) — highly repetitive “jumping” genes that have been duplicated throughout the genome.
This massive accumulation of non-coding DNA raises fascinating questions about the role of these TEs. While traditionally thought of as “junk” DNA, researchers believe that these elements may play a significant part in allowing organisms to adapt to environmental changes. By adjusting the expression of specific genes, TEs can promote rapid evolutionary changes, giving the lungfish an edge in survival over millions of years.
The Cost of Carrying Extra DNA
Despite the adaptive potential offered by such a massive genome, there are drawbacks. Evolutionary biologist Axel Meyer of the University of Konstanz points out that maintaining such a large amount of DNA is costly for the organism. The lungfish’s chromosomes, with 19 in total, include one that is the size of the entire human genome. Copying this enormous amount of genetic material requires significant energy, and the nucleus and cells that house the DNA must be larger as a result.
Nonetheless, the lungfish has thrived, thanks in part to its ability to suppress TEs with specific genes. Scientists believe these genes were inherited from ancient viral infections, which helped the fish manage the rapid expansion of its genome over the last 100 million years.
A Record-Setting Genome – But Not for Long?
While the South American lungfish currently holds the title of the world’s largest animal genome, it may soon lose this distinction. The marbled lungfish (Protopterus Aethiopicus) is suspected of having a genome that is 50% larger, but this has yet to be confirmed through sequencing. If true, it would set a new record for genome size within the animal kingdom.
However, the lungfish is not the absolute largest genome in nature. That honor belongs to a peculiar species of fern, which harbors an astonishing 160 billion base pairs—more than 50 times the size of the human genome.
Understanding Genomic Evolution
The sequencing of the South American lungfish genome provides more than just record-breaking statistics. It offers insights into the evolutionary mechanisms that drive genome expansion across the tree of life. As scientists continue to decode the genetic mysteries of species like the lungfish, they uncover how organisms adapt, evolve, and thrive over millions of years.
With advancements in genomic sequencing technology, the door is now open to further explore the largest animal genomes and other genetic wonders that shed light on the fascinating history of life on Earth.
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