Researchers at the National Human Genome Research Institute (NHGRI), part of the U.S. National Institutes of Health (NIH), have managed to produce the first end-to-end DNA sequence of a human chromosome. The whole genome sequencing results were recently published in the journal Nature (read HERE)

“This accomplishment begins a new era in genomics research,” said Eric Green, director of NHGRI. “The ability to generate truly complete sequences of chromosomes and genomes is a technical feat that will help us gain a comprehensive understanding of genome function and inform the use of genomic information in medical care.”

Although the human genome sequence has so far been the most accurate and complete ever produced for vertebrates, there are still hundreds of gaps or DNA sequences that are unknown. These gaps often contain repetitive DNA segments that are exceptionally difficult to sequence. Nevertheless, these repetitive segments include genes and other functional elements that may be relevant to human health and disease.

Methodology to obtain the whole genome sequencing

The human genome consists of about 6 billion bases, which DNA sequencing machines cannot read at once. Instead, researchers chop the genome into smaller pieces and analyze each piece to yield sequences of a few hundred bases. These shorter DNA sequences must then be put back together, which is sometimes too complex. In the study discussed herein, new technologies were used that can sequence long segments of DNA. Instead of preparing and analyzing small pieces of DNA, they used a method that leaves the DNA molecules largely intact. These large DNA molecules were then analyzed by two different instruments. Each of them generates very long DNA sequences, something that previous instruments could not do. The researchers then used their newly developed software to assemble the many segments of generated sequences.

Of the 24 human chromosomes (including X and Y), the X chromosome sequence has been completed first, due to its link with a myriad of diseases, including hemophilia, chronic granulomatous disease, and Duchenne muscular dystrophy. The group has managed to close the largest remaining sequence gap on the X chromosome, the approximately 3 million bases of repetitive DNA found in the middle portion of the chromosome, called the centromere.

Complete reference sequence of the human genome

The effort is part of a broader initiative by the Telomere-to-Telomere (T2T) consortium, partially funded by the NHGRI. The consortium aims to generate a complete reference sequence of the human genome. The T2T consortium is continuing its efforts with the remaining human chromosomes, with the aim of generating a complete human genome sequence in 2020. The researchers say that finishing the entire human genome is now within our reach.

Benefits and risks

In our view, this is a breakthrough that will allow us to develop a clearer understanding of something that has thus far been obscure, and that may have great medical benefits. While it is true that these discoveries can also bring us closer to scientific realities such as the production of designer babies, it is our responsibility to use this knowledge for the true good of the person.

(Source: National Institutes of Health https://www.nih.gov/news-events/news-releases/nih-researchers-generate-complete-human-x-chromosome-sequence).