Why in the news?

• Nearly two decades ago, when scientists published the map of the human genome for the first time, it was hailed as a breakthrough. That was incomplete, however: about 8% of the human DNA was left unsequenced.
• Now, in a series of papers published in Science, a large team has accounted for that 8%, completing the picture of the human genome for the first time.

Why it matters

• A complete human genome makes it easier to study genetic variation between individuals or between populations.
• A genome refers to all of the genetic material in an organism, and 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 disease.

What was missing

• The genetic sequence made available in 2003 from the Human Genome Project, an international collaboration between 1990 and 2003, contained information from a region of the human genome known as the euchromatin. Here, the chromosome is rich in genes, and the DNA encodes for protein.
• The 8% that was left out was in the area called heterochromatin. This is a smaller portion of the genome, and does not produce protein.
• There were at least two key reasons why heterochromatin was given lower priority. This part of the genome was thought to be “junk DNA”, because it had no clear function. Besides, the euchromatin contained more genes that were simpler to sequence with the tools available at the time.
• Now, the fully sequenced genome is the result of the efforts of a global collaboration called the Telomere-2-Telomere (T2T) project.
• The invention of new methods of DNA sequencing and computational analysis helped complete the reading of the remaining 8% of the genome.

What’s in the 8% and its significance

• The new reference genome, called T2T-CHM13, 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 new sequence also reveals long stretches of DNA that are duplicated in the genome and are known to play important roles in evolution and disease.
• The new T2T reference genome will complement the standard human reference genome, known as Genome Reference Consortium build 38 (GRCh38), which originated from the Human Genome Project and has been updated since.

Reference:

1. https://indianexpress.com/article/explained/complete-human-genome-explained-7848706/