Washington, April 1 (BUS): Scientists say they have finally assembled the complete genetic blueprint for human life, adding the missing pieces to a puzzle almost completed two decades ago, according to the Associated Press.
An international team described the first-ever sequence of a complete human genome – the set of instructions for building and maintaining a human – in research published Thursday in the journal Science.
The earlier effort, celebrated around the world, was incomplete because DNA sequencing technologies at the time were not able to read certain parts of it. Even after updates, about 8% of the genome was lost.
“Some of the genes that make us uniquely human were actually in this ‘dark matter of the genome’ and were completely overlooked,” said Evan Eichler, a researcher at the University of Washington who was involved in the current effort and the original Human Genome Project. “It took more than 20 years, but we finally got it done.”
This complete picture of the genome will give humanity a greater understanding of our evolution and biology, the scientists said, while also opening the door to medical discoveries in areas such as aging, neurodegenerative conditions, cancer and heart disease.
Research culminates 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 entities: an international publicly funded project led by an agency of the US National Institutes of Health and a private company, Maryland-based Celera Genomics.
The human genome is made up of about 3.1 billion DNA subunits, pairs of chemical bases known as the letters A, C, G, and T. Genes are chains 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 that are located in the nucleus of each cell.
Before now, Mega said there were “large and persistent gaps in our map, and these gaps are located in very important areas.”
Mega, a genomics researcher at the University of California, Santa Cruz, worked with Adam Philip of the National Human Genome Research Institute to organize the team of scientists to start from scratch with a new genome with the goal of sequencing all of it, including previously the missing pieces.
The group, named after the sections at the ends of chromosomes called telomeres, is known as the telomere-to-telomere union, or T2T.
Their work adds new genetic information to the human genome, corrects previous errors and reveals long stretches of DNA known to play important roles in both development and disease.
Eichler said that some scientists believed that unknown areas contained “junk.” not him. “Some of us always thought there was gold in those hills,” he said. Eichler is paid by the Howard Hughes Medical Institute, which also supports the Associated Press’s Department of Health and Science.
It turns out that gold contains many important genes, he said, such as those that are integral to making a person’s brain larger than a chimpanzee’s, with more neurons and connections.
To find such genes, scientists needed new ways to read the hidden genetic language of life.
Reading genes requires cutting DNA strands into pieces hundreds to thousands of letters long. Sequencing machines read the letters in each piece and scientists try to arrange the pieces in the correct order. This is especially difficult in areas where the letters are repeated.
Some regions were illegible before improvements in genetic sequencing machines that now allow them, for example, to accurately read a million letters of DNA at a time, the scientists said. This allows the scientists to see genes with repeating regions as longer chains rather than snippets that they later had to put together.
The researchers also had to overcome another challenge: Most cells contain both maternal and paternal genomes, confusing attempts to properly assemble the pieces.
The T2T researchers were able to get around this by using a cell line from a “complete hydatidiform mole,” an abnormal fertilized egg with no fetal tissue that contains two copies of the father’s DNA and no two copies of the mother’s DNA.
next step? Mapping more genomes, including those that include combinations 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 contains only an X.
Wang said he is working with the T2T group at the Pangenome Human Reference Consortium, which is trying to create “reference” or model genomes for 350 individuals that represent the breadth of human diversity.
“Now we’ve got one correct genome and we have to do a lot, a lot more,” Eichler said. “This is the start of something really cool in the field of human genetics.”
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