Explained: The complete human genome, and what it tells us

What is the News?

In 2003, Scientists had published the map of the human genome for the first time. However, this was incomplete as about 8% of the human DNA was left unsequenced. 

Now, a large global collaboration called the Telomere-2-Telomere(T2T) project has accounted for the remaining 8% and completing the picture of the human genome for the first time.

What is Genome and why Human Genome matter?

A genome refers to all of the genetic material in an organism. The Human genome is mostly the same in all people, but a very small part of the DNA does vary between one individual and another. 

By constructing a complete human genome, scientists can use it for reference while studying the genome of various individuals, which would help them understand which variations if any, might be responsible for the disease.

When was the Human Genome Sequencing done and what was missing?

Human Genome Sequencing was made available in 2003 by the Human Genome Project, an international collaboration between 1990 and 2003.

It contained information from a region of the human genome known as the euchromatin. This chromosome is rich in genes, and the DNA encodes for protein.

The remaining 8% that was left out was in the area called heterochromatin. This is a smaller portion of the genome and does not produce protein.

Why was heterochromatin not sequenced?

There were two key reasons why heterochromatin was given lower priority:  1) This part of the genome was thought to be “junk DNA” because it had no clear function, 2) The euchromatin contained more genes that were simpler to sequence with the tools available at the time.

What has been done now?

A global collaboration called the Telomere-2-Telomere (T2T) project has completed the reading of the remaining 8% of the genome.

They found a new reference genome called T2T-CHM13. This genome includes highly repetitive DNA sequences found in and around the telomeres (structures at the ends of chromosomes) and the centromeres (at the middle section of each chromosome). 

The sequence also reveals long stretches of DNA that are duplicated in the genome and are known to play important roles in evolution and disease.

Source: This post is based on the article “Explained: The complete human genome, and what it tells us” published in Indian Express on 2nd April 2022.