The saga of deciphering our genome is coming to an end. “It took twenty-five to thirty years to achieve this”, notes Philippe Froguel, professor of genetics at the University of Lille and Imperial College London. On March 31, in fact, the magazine Science published six major articles: a consortium of American researchers announced that they had succeeded in reading the hitherto unexplored regions of our DNA. “Be, in size, the equivalent of a small chromosome”, specifies Philippe Froguel. Only the male Y chromosome will remain, which is not part of this corpus.
It all started on February 16, 2001. On that day, magazines Nature and Science publish, each on its own, the “big book” of the human genome. A feat at the exorbitant cost of 3 billion dollars, hailed all around the globe, which marks the accomplishment of more than ten years of effort, uniting the forces of more than a hundred academic researchers around the world – the firm private company Celera Genomics having also entered the race. Thanks to which the researchers had deciphered the sequence of some 3 billion “chemical letters” etched in our DNA.
Except that this original edition remained a draft, riddled with errors and dotted with blanks. Between 2001 and today, 38 editions of “reference human genome” will be published in turn. So many updates which, little by little, made it possible to correct errors and fill in gaps. But now, 8% of our genome remained unreadable. For two reasons: these nebulous pages are ultra-coiled and covered with ultra-repeated words. 90% of them are found in the centromeres (in the center of our chromosomes). The rest is nestled in the telomeres (at the ends of our chromosomes) or scattered throughout the genome.
“ancestral patterns”
Thanks to a new sequencing method, this ultra-repeated DNA could be read by the Telomere-to-Telomere (T2T) consortium, created three years ago. Partly funded by the American Institutes of Health (NIH), it involves 33 institutions and universities, mainly in the United States. As always for a reference genome, the T2T consortium focused on the sequencing of a single human genome: here, a cell line from a non-viable human embryo, called a “hydatidiform mole”.
What will be the applications of this complete cartography? Analyze the functions of these ultra-repeated DNA sequences, first. Those are « elephant graveyards », notes Stanislas Lyonnet, director of the Imagine institute of genetic diseases on the Necker campus (AP-HP, Inserm, University of Paris). Except that here the elephants are rather viruses, disappeared for ages. The DNA made from their RNA, in the cells of people who were infected in the past, has gradually integrated into our genome. But what is the current role of these “ancestral patterns” ?
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