Sequencing the entirety of the human genome is an enormous undertaking that would drastically improve our understanding of ourselves, especially regarding disease and evolution.
More than two decades ago, the Human Genome Project began to unravel the mysteries of the human genome, publishing its first draft in 2000, and then another in 2003 which offered us a “complete” genome. However, this complete genome only included euchromatic regions, which make up around 92 percent of the total genome.
The other eight percent were the heterochromatic regions, found in the tips and centers of the chromosomes, which could not be sequenced at that time as it would be too difficult and expensive.
Now, however, an international team of scientists known as the Telomere-to-Telomere (T2T) succeeded in completing the first gap-free sequence of the human genome—that’s around three billion bases! The breakthrough is so big that it could not only be discussed in one paper alone but in a series of six papers published in the journal Science, along with several other papers in other journals.
Not only does this new reference genome (dubbed the T2T-CHM13) add nearly 200 million base pairs that were previously unknown DNA sequences, but it corrects the thousands of structural errors of earlier versions.
How did they do it?
Even though the team was only working on the remaining eight percent of the human genome, they reported that it took twice as long to sequence as the first 92 percent. To do this meticulous work, the researchers used a combination of the Oxford Nanopore DNA sequencing method, which can read up to a million DNA letters in a single read with moderate accuracy, and the PacBio HiFi method, which can read around 20,000 letters in one read with almost perfect accuracy.
Having a human genome sequenced in its entirety will help countless future studies, including those surrounding genetic markers of disease. A deeper understanding of the heterochromatic regions will also help in the fight against cancer, which often arises from abnormalities in the center of the chromosome.
“Generating a truly complete human genome sequence represents an incredible scientific achievement, providing the first comprehensive view of our DNA blueprint,” said director of National Human Genome Research Institute Eric Green, M.D., Ph.D. “This foundational information will strengthen the many ongoing efforts to understand all the functional nuances of the human genome, which in turn will empower genetic studies of human disease.”
Source study: Science—The complete sequence of a human genome