Scientists managed to fully assemble the human X-chromosome. This happened for the first time.

The complete assembly of the human X chromosome is a landmark achievement for genomics researchers.

Lead author of the study, Karen Miga ofCalifornia Institute of Genomics in Santa Cruz, said the project was made possible thanks to new sequencing technologies. Nanopore technology, which allows sequencing of long segments of DNA, leaves the molecules intact.

Duplicate DNA Sequencesdistributed throughout the genome and always posed a challenge for sequencing. Most technologies produce relatively short “readings” of the sequence, which then need to be put together, like a mosaic to assemble the genome. Repeating sequences lead to many short reads and they look almost the same. It remains a mystery how different parts of the genome fit together or how many of their repetitions.

These repeating sequences oncewere considered insoluble, but now we have made a breakthrough in sequencing technology. Thanks to nanoporous sequencing, we get extra-long readings of hundreds of thousands of base pairs, which can cover the entire repeating area, which allows you to bypass some problems.

Karen Miga, researcher at the California Institute of Genomics in Santa Cruz

Fill in the remaining gaps inThe sequence of the human genome opens up new areas. Now scientists have the opportunity to look for connections between sequence variations and a specific disease, as well as other keys to important issues of biology and human evolution.

Although the reference sequenceThe human genome was created about 20 years ago; there are still hundreds of gaps in it. Yes, most DNA sections are repeated, but missing segments may include functional elements related to certain diseases.

Scientists emphasize that many of the inaccessibleearlier parts of the genome are among the richest for variations in human populations. This information may be important for understanding general human biology.

Karen Miga and Adam Phillippy of the NationalThe Human Genome Research Institute (NHGRI) co-founded a telomere-telomere consortium (T2T) to conduct a complete genome assembly. Previously, they worked together on a 2018 document that demonstrated the potential of nanopore technology to obtain the complete sequence of the human genome. For their purposes, scientists used the MinION Oxford Nanopore Technologies sequencer. It captures current changes that occur when individual DNA molecules pass through nanopores in the membrane. After that, the researchers once again analyzed these large DNA molecules on two different instruments, each of which generates very long sequences.

Scientists usedown computer program for assembling many segments of the generated sequences. Using technology, the team created an assembly with a whole human genome that surpasses all previous assemblies in terms of continuity, completeness and accuracy. Continuous assembly even surpasses the current reference human genome in some respects.

However, according to scientists, there were still several interruptions in this sequence. To complete the X chromosome, the team had to manually eliminate several gaps in the sequence.

The new sequence of the human genome,derived from a human cell line called CHM13 closes many gaps in the current reference genome known as the Genome Reference Consortium build 38 (GRCh38).

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