First gap-free sequencing of the human genome

Why in news?

• Scientists map a full human genome for the first time, including previously hard-to-read 'junk DNA' that could contain clues about conditions from autism to aging.

More about 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 (some called it ‘junk DNA’).
• 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?

• A genome, simply put, is all the genetic matter in an organism. It is defined as an organism’s complete set of DNA, including all of its genes.
• Each genome contains all of the information needed to build and maintain that organism.
• In humans, a copy of the entire genome - more than 3 billion DNA base pairs- is contained in all cells that have a nucleus.
• 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.

Why Human Genome matter?

• A complete human genome makes it easier to study genetic variation between individuals or between populations.
• 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.

PRACTICE QUESTION:

With reference to ‘Dark Genome’, consider the following statements:

1. It cannot be adequately assembled or aligned using standard short-read sequencing technologies

2. It does not encode proteins

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer