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Scientists say they’ve finally put together the complete genetic blueprint for human life and added the missing pieces to a puzzle that was completed almost two decades ago.
An international team has described for the first time sequencing a complete human genome — a set of instructions for building and maintaining a human — in research published Thursday in the journal Science. The previous effort, celebrated around the world, was incomplete because the DNA sequencing technologies of the day could not read certain parts of it. Even after the updates, about 8% of the genome was missing.
“Some of the genes that make us uniquely human were actually in this ‘dark matter of the genome’ and have been completely overlooked,” said Evan Eichler, a University of Washington researcher who participated in the current effort and the original Human Genome Project. “It took more than 20 years, but we finally made it.”
Many – including Eichler’s own students – thought it was over anyway. “I was teaching them and they said, ‘Wait a minute. Isn’t this the way you declared victory for the sixth time? I said, ‘No, we really, really made it this time.
The scientists said this complete picture of the genome will give humanity a better understanding of our evolution and biology, while also opening the door to medical discoveries in areas such as aging, neurodegenerative conditions, cancer and heart disease.
“We’re expanding our opportunities to understand human diseases,” said Karen Miga, author of one of six studies published Thursday.
The research spans decades of work. The first draft of the human genome was announced at a White House ceremony in 2000 by the leaders of two competing organizations: a publicly funded international project led by an agency of the US National Institutes of Health and a private company based in Maryland called Celera Genomics.
The human genome consists of approximately 3.1 billion DNA subunits, chemical base pairs known by the letters A, C, G, and T. Genes are sequences of these letter pairs that contain instructions for making proteins, the building blocks of life. Humans have about 30,000 genes organized into 23 groups called chromosomes located in the nucleus of each cell.
Before that, “we had large and persistent gaps in our map, and these gaps fall into some pretty important areas,” Miga said.
Miga, a genomics researcher at the University of California-Santa Cruz, worked with Adam Phillippy of the National Human Genome Research Institute to organize the team of scientists to start from scratch with a new genome to sequence them all, including before. lost parts. The group, named after the ends of the chromosomes called telomeres, is known as the Telomere-Telomere or T2T consortium.
Their work adds new genetic information to the human genome, corrects previous errors, and uncovers long DNA sequences known to play important roles in both evolution and disease. A version of the research was published last year before it was reviewed by scientific colleagues.
“I would say it’s a major breakthrough that doubles the impact of the Human Genome Project,” said geneticist Ting Wang of the Washington University School of Medicine in St. Louis, who was not involved in the research.
Eichler said some scientists think the unknown areas contain “garbage.” not him. “Some of us always believed there was gold in those hills,” he said. Eichler is paid by the Howard Hughes Medical Institute, which also supports the Associated Press’s health and science division.
It turns out that gold contains many important genes, such as those integral to making a person’s brain bigger than a chimpanzee’s, with more neurons and connections.
To find such genes, scientists needed new ways to read the cryptic genetic language of life.
Reading genes requires breaking up strands of DNA into segments hundreds to thousands of letters long. Sorting machines read the letters on each piece, and scientists try to put the pieces in the correct order. This is particularly difficult in areas where letters are repeated.
Scientists said some areas were illegible before advances in gene sequencing machines, for example, that allowed them to accurately read a million letters of DNA at a time. This allows scientists to view genes with repeated domains as longer sequences, rather than as particles that they then have to put together.
The researchers also had to overcome another challenge: Most cells contain genomes from both maternal and paternal genes, which confuses attempts to assemble the pieces correctly. The T2T researchers tackled this issue by using a “complete hydatidiform mole” cell line, which is an abnormally fertilized egg with two copies of the father’s DNA and none of the mother’s, with no fetal tissue.
Next step? Mapping more genomes, including those containing collections of genes from both parents. This effort did not map one of the 23 chromosomes found in males, called the Y chromosome, because the mole contained only one X.
Wang said he’s working with the T2T group at the Human Pangenome Reference Consortium, which is trying to create “reference” or template genomes for 350 individuals that represent the breadth of human diversity.
“Now we have an accurate genome and we need to do a lot more,” Eichler said. “This is the beginning of something truly amazing for the field of human genetics.”
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