Scientists almost finished sequencing human DNA

(ORDO NEWS) — Biologists have sequenced the last percent of the human genome that has not yet been fully sequenced.

The international consortium T2T announced the successful completion of the work. Twenty years after the sequence of the human genome was determined, scientists figured out the remaining sections about eight percent, which were the most difficult to sequence.

The human genome was almost completely identified back in 2003, as part of the global study of the Human Genome Project. For that time, the task was daunting, and hundreds of researchers from different universities and countries participated in its solution.

They have successfully sequenced about 92 percent of the DNA the genes and the regions in between that make up euchromatin. In cells, euchromatin is actively working, so it remains “untwisted” and twists into a more compact form only for division.

Unlike it, heterochromatin constantly retains a compact shape and does not encode proteins. It primarily performs auxiliary functions, maintaining the structure and integrity of chromosomes, ensuring their interaction with proteins, and the like.

Heterochromatin is located, for example, in centromeres the regions where a pair of sister chromosomes join to form the recognizable “X” and in telomeres, the ends of chromosomes. This DNA is characterized by the presence of long repetitive sequences, the definition of which is a big problem.

Recall that for sequencing, a DNA strand must be cut into many fragments, then the nucleotide sequence of each of them must be determined, and finally, the resulting codes must be connected in the correct original order.

But if the code is hundreds of indistinguishable short repetitions, such work becomes almost impossible. That is why the participants of the Human Genome Project had to skip this small part of the genome for the benefit of the tasks of science and medicine, it plays far from the main role.

However, a complete understanding of the structure of the genome requires at least complete sequencing, and over time, sequencing technologies have made great strides forward.

Therefore, a new consortium , Telomere to Telomere (T2T), began work a few years ago, setting itself the task of sorting out sections of heterochromatin. In 2021, its participants presented a “rough” result, and now the final one, covering the missing eight percent of the genome.

To do this, biologists had to resort to a little trick, using DNA from a cell line with an inherited disorder to sequence it, as a result of which they carry two identical copies of each chromosome (instead of one maternal and one paternal).

Therefore, the T2T consortium has not completed its work: at least its participants have yet to sequence heterochromatin on the unpaired Y chromosome.

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