In June 2000, the Human Genome Project and Celera Genomics Corporation announced the completion of work on the sequencing of the human genome. In February 2001, they published a draft of the genome.
By October 2004, scientists had published the final sequencing results in the journal Nature. In the course of the work, the researchers formed DNA sequences that contained approximately 90% of the human genome. In other words, their work was not complete.
Since the completion of the Human Genome Project in 2000, researchers have created several genomic reference books. Scientists made the last major update in 2017, where they supplemented the GRCh38 reference book created in 2013 and corrected about a thousand errors in the compiled sequences.
At the same time, GRCh38 is also incomplete – about 8% of the genome was missing not because scientists hadn’t tried to map it but due to technological disabilities. Now, with advanced sequencing technologies, scientists claim to have successfully sequenced the entire human genome.
Everything you need to know about the new complete human genome sequencing and why it is important
1. In a new study, specialists from the international consortium Telomere-to-Telomere (T2T) worked on unidentified regions of the genome and filled in the gaps with the data obtained. According to the researchers, they have compiled a complete guide to the T2T-CHM13 human genome.
2. The authors used long-read sequencing methods: single-molecule PacBio HiFi and nanoporous Oxford Nanopore in combination with an almost completely homozygous CHM13hTERT (CHM13) line. The researchers designated the first draft genome assembly as CHM13v0.9.
3. Later, ten megabases with rRNA genes were added to it and a complete CHM13v1.1 assembly was obtained. The average build accuracy was between Phred Q67 and Q73 (one error per ten megabases). This means that the researchers did not cover regions with low coverage – only 0.3% of the genome.
4. In T2T-CHM13, the authors included a gap-free assembly of 22 human autosomes and the X chromosome, including over 3 billion nucleotide pairs of nuclear DNA and 16 thousand nucleotides of the mitochondrial genome. This is 200 million base pairs more than GRCh38.
5. There is no Y chromosome data in the new handbook because the researchers took samples from a woman with a molar pregnancy to study. With this type of pathology, the defective egg does not contain a nucleus with its own chromosomes, therefore, after fertilization, two copies of a set of 23 paternal chromosomes remain inside.
6. From such eggs, instead of embryos, bubble drifts appear. The researchers said they are already working on the HG002 cell line with 46 XY karyotypes.
7. Other scientists have raised concerns about the CHM13 cell line. Since the authors froze and stored the cell culture in the laboratory for some time, cell detritus (dead organic matter) may have been present in CHM13.
8. Therefore, detritus data may be present in T2T-CHM13. The authors argue that they conducted a thorough analysis before genome sequencing and rule out this possibility.
9. Researchers use complete genome sequencing for genetic research in a variety of fields. For example, in May of this year, anthropologists, based on DNA analysis, determined the differences between cell metabolism in Neanderthals and modern humans. In addition, genome sequencing is used by physicians to diagnose, treat, and predict genetic diseases.
10. If successfully peer-reviewed, the T2T-CHM13 study will become the most comprehensive reference for the human genome. According to the researchers, based on the data obtained, it is already possible to trace the regulation of genes and look for new relationships in the work of different parts of the genome.
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