The Enigma of the Largest Genome: A Tiny Fern's Record-Breaking DNA
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Chapter 1: Introduction to Tmesipteris oblanceolata
Recent discoveries have unveiled an extraordinary species of fern that boasts an astonishing amount of DNA—up to 50 times more than that found in human cells. This remarkable plant, known as Tmesipteris oblanceolata, has even earned a spot in the Guinness World Records for its unique genetic makeup.
Located in New Caledonia, a French territory in the Pacific, T. oblanceolata is an endemic species that has captured the attention of scientists worldwide. A recent study published in the journal “iScience” by researchers from the Royal Botanic Gardens, Kew, and the Botanical Institute of Barcelona has confirmed that this fern possesses the largest genome of any known living organism.
Section 1.1: The Findings of the Research
In an expedition to New Caledonia, lead researchers Dr. Jaume Pellicer and Dr. Oriane Hidalgo collected samples of T. oblanceolata for analysis to determine the size of its genome. The results revealed that each cell contains approximately 321 billion nucleotide pairs in its nucleus.
Each nucleotide consists of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), cytosine (C), guanine (G), or thymine (T). In comparison, human DNA holds about 3 billion nucleotide pairs. If transcribed, the sequence of human nucleotides would fill numerous volumes, whereas the fern's genome would stretch to a remarkable 105 meters, exceeding the length of a football field.
Breaks all records: World's largest genome found in small fern | REUTERS - YouTube
Section 1.2: The Previous Record Holder
Before this discovery, the title of the largest genome was held by Paris japonica, a rare plant native to Japan with over 149 billion base pairs. Among animals, the marbled lungfish has the largest known genome, featuring 260 billion base pairs.
Dr. Pellicer explains that several factors contribute to the immense size of certain plant genomes. Notably, many plants possess multiple sets of chromosomes—unlike animals, which typically have only two. T. oblanceolata, for example, has up to eight sets. He notes, however, that while many polyploid plants have relatively small genomes, a significant factor in this case is the unchecked growth of genetic mutations known as transposons.
Understanding Transposons and Their Impact
Transposons are segments of DNA that can shift positions within a genome, often leading to mutations and alterations in DNA quantity. However, Dr. Pellicer warns that possessing such a massive genome may not necessarily be beneficial.
"Every time a cell divides, it must replicate all its DNA, which can lead to longer replication times," he explains. He adds that plants lacking control over transposons often face extinction, a fate that T. oblanceolata has avoided due to its relatively low competition in its habitat.
Chapter 2: The Implications of the Discovery
The groundbreaking discovery of T. oblanceolata's genome has led to its recognition in the Guinness World Records three times: for the largest plant genome, the largest genome overall, and the largest genome for a species based on nuclear DNA content.
New Caledonia: World's Largest Genome Found In Small Fern - YouTube
Dr. Pellicer emphasizes the remarkable evolutionary history of Tmesipteris, which has roots tracing back 350 million years, long before the era of dinosaurs. Initially, researchers doubted that any species could surpass the genomic size of Paris japonica, yet this fern continues to challenge our understanding of biology and genetics.
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