In today’s edition of Current Affairs Dialog box, we will discuss Human Genome and its relevance to the UPSC CSE syllabus. The topic is crucial from the UPSC exam preparation point of view. Hence, it should be studied in depth.

For Prelims: General Science

For Mains: Science and Technology- Developments and their Applications and Effects in Everyday Life

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Probable Question

Examine the significance of the Human Genome Project in studying genetic variation of populations.

Why in the News?

Recently, a team of scientists has sequenced the leftover 8 percent of the Human Genome. 

Key Points

Background

• In the early 2000s, about 92 percent of the genome had been decoded under the Human Genome Project. Now, the remaining eight percent has been sequenced. The findings are described in six papers in the journal, Science.
• This fully sequenced genome is the result of the efforts of a global collaboration called the Telomere-2-Telomere (T2T) project.
• In the Telomere-2-Telomere (T2T) project, scientists have decoded the DNA in the heterochromatic region of the genome while the Human Genome Project decoded DNA present in the euchromatin region of the genome.

Image Source: The Financial Express

Why was Heterochromatin Left Out in the Human Genome Project?

• Initially, scientists deprioritized heterochromatin. Since the euchromatic regions contained more genes and were simpler to sequence, the genomic tools available at that time found euchromatic DNA easier to parse compared to heterochromatic DNA. 
• In simple words, advanced tools to decode heterochromatin were not available. Those tools were developed over the years. 

Heterochromatin: Heterochromatin is non-coding DNA that does not make protein but still plays crucial roles in many cellular functions.  Since heterochromatin does not make protein, it was thought to be junk DNA. Euchromatin: It is a lightly packed form of chromatin (a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells) that is enriched in genes, and easily transcribed. In other words, euchromatin creates protein.

Telomere-2-Telomere (T2T) Project

• With laboratory techniques, computational biology approaches, and other essential research resources, scientists have decoded the DNA in heterochromatin. 
• 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 findings have revealed a large number of genetic variations, and these variations appear in large part within these repeated sequences.

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Human Genome Project: Human Genome Project (HGP) began in 1990 and reached completion in 2003.  Project Coordination: The National Institutes of Health and the US Department of Energy. HGP was undertaken with the aim of sequencing the human genome and identifying the genes that contain it.  In it, DNA from a region called euchromatin was sequenced while that from a region called heterochromatin was left out.  Euchromatin is a lightly packed form of chromatin (a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells) that is enriched in genes, and easily transcribed.  The project was able to identify the locations of many human genes and provide information about their structure and organisation.

What is a Genome?

• A genome is the complete set of genetic information in an organism and provides all of the information the organism requires to function. 
• The genome of living organisms is stored in long molecules of DNA (deoxyribonucleic acid) called chromosomes.
• In humans, a copy of the entire genome — more than 3 billion DNA base pairs — is contained in all cells that have a nucleus”.

Significance

• 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.
• The complete sequence will be valuable for studies that aim to establish comprehensive views of human genomic variation. 
• 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.
• Genome mapping is helpful in figuring out the location of a specific gene on a particular region of the chromosome.
• Genome mapping enables scientists to gather evidence if a disease transmitted from the parent to the child is linked to one or more genes.

News Source: The Hindu

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