An international team of researchers, including human geneticists at the Howard Hughes Medical Institute at the University of Washington in Seattle, have used new DNA sequencing technology (deoxyribonucleic acid, a complex chemical in almost all organisms that carries genetic information), to unravel repetitive stretches of DNA that were redacted from an earlier version of the genome.
DNA is made up of four building blocks called nucleotides, each indicated by a letter. They are adenine (A), thymine (T), guanine (G), and cytosine (C).
Now, after sequencing the roughly 8% that were missing , according to earlier versions of the genetic instruction book, researchers have succeeded in sequencing an entire human genome; no gaps. And it is now available to scientists and the general public, marking a great moment in the history of human genetics.
Up to six articles have been published in the journal Science that describe, one by one, the meticulous work involved in sequencing a genome of more than 6 billion base pairs, with 200 million added in this new research. This new genome has added 99 likely protein-coding genes and 2,000 previously unknown candidate genes.
It is the story of hard work over time: in 2000, the Human Genome Sequencing Consortium published its first drafts of the human genome, but it has taken us another twenty years to complete it due to the limitations of sequencing technologies. of DNA . Now, new developments have made it possible to fill in the gaps and have helped reveal hitherto unknown parts of the genome.
“These parts of the human genome that we haven’t been able to study for more than 20 years are important for understanding how the genome works, genetic diseases, and human diversity and evolution,” explains Karen Miga of the University of California and co-author of one of the studies.
All in caps. And their efforts have paid off.
The work was conducted by the Telomere to Telomere (T2T) consortium, which included researchers from the National Human Genome Research Institute (NHGRI); the University of California, Santa Cruz (UCSC); and the University of Washington, Seattle (USA).
The newly completed genome has been dubbed T2T-CHM13 , and is available through the UCSC Genome Browser online.
Of course, according to the authors, the recently completed genome does not have gaps like the previous reference human genome, but it still has limitations. The ancient genome was a conglomeration of the DNA of more than 60 people. The new genome does not come from a person either : it is the genome of a complete hydatidiform mole, a kind of tumor that arises when a sperm fertilizes an empty egg and the father’s chromosomes are duplicated (a molar pregnancy resulting in an abnormal fetus).
Thus, what has been completed is “a” human genome, not “the” human genome.
Having a map of where all genes are located can lead to a better understanding of how they work, and perhaps even what makes humans human.
The next step
Looking ahead, scientists hope to add more reference genomes as part of the Human Pangenome Reference Consortium to improve diversity in human genetics, something that is really needed today.
“We are including a second complete genome, and there will be more to come,” David Haussler, director of the UC Santa Cruz Genomics Institute, said in a statement. “The next phase is to think of the reference genome of humanity as if it were not a single genomic sequence. This is a profound transition, the harbinger of a new era in which we will finally grasp human diversity in an unbiased way.”
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