Genome Editing: Techniques, Applications and Human Genome Project

Genome editing, also known as genome engineering or gene editing, is a sophisticated form of genetic engineering that enables precise alterations in an organism’s DNA, including insertion, deletion, modification, or replacement of genetic material.

Genome Editing: Techniques and Applications in Modern Science

• Genome editing, also known as genome engineering or gene editing, is a sort of genetic engineering that involves inserting, deleting, modifying, or replacing DNA in a living organism’s genome.  

                                                                                                            Fig: Genome editing

Genome Editing Techniques [UPSC 2020] 

• Clustered regularly interspaced short palindromic repeats (CRISPR)– CRISPR- associated protein 9 (Cas9): CRISPR is the DNA-targeting component of the system, and it is made up of an RNA molecule, or guide, that is engineered to attach to certain DNA bases via complementary base-pairing.
  • CRISPR-associated protein 9 (Cas9) is the nuclease component that cuts the DNA.
  • The CRISPR-Cas9 genetic scissors were discovered by Emmanuelle Charpentier and Jennifer A. Doudna, who won the Nobel Prize in Chemistry in 2020. [UPSC 2019]

• Transcription activator-like effector nucleases (TALENs): Transcription activator-like effector (TALE) domains make up the DNA-binding domain of TALENs. 
• Zinc-finger nucleases (ZFNs): ZFNs are fusions between a custom-designed Cys2-His2 zinc-finger protein and the cleavage domain of the FokI restriction endonuclease. FokI cleavage domain, which cuts DNA within a five- to seven-bp spacer sequence that separates two flanking zinc-finger binding sites. 
• Homing endonucleases or mega-nucleases: Homing endonucleases, also known as mega-nucleases.
  • These enzymes make extensive sequence-specific contacts with their DNA substrate. 
  • However, unlike ZFNs and TALENs, the binding and cleavage domains in homing endonucleases are not modular. 
  • This overlap in form and function makes their repurposing challenging and limits their utility for more routine applications of genome editing.

Significance of Genome Editing

• These techniques affect different areas such as disease management, basic biomedical research, agriculture and environmental sciences. 
• They could also be used to customise human characteristics for extra-therapeutic enhancement purposes. 

Human Genome Project [UPSC 2011]

• About: In the 1980s, scientists began discussing the possibility of sequencing all 3.2 billion nucleotide pairs in the human genome.
• These discussions led to the launch of the Human Genome Project in 1990. The initial goals of the Human Genome Project were:
  • To map all the human genes,
  • To construct a detailed physical map of the entire human genome, and
  • To determine the nucleotide sequence of all 24 human chromosomes by the year 2005.

General Features of the Human Genome

• Entire human genome contains about 3.2 billion base pairs of DNA.
• Base-pair composition of the DNA varies across regions of the human genome.
• Composition: On average, about 41 per cent of the DNA consists of G: C base pairs. 
  • However, some regions are G: C rich, and others are G: C poor.

Conclusion:

Genome editing represents a leap in our ability to manipulate genetic material, offering unprecedented opportunities for scientific and medical advancements. Techniques like CRISPR-Cas9, TALENs, and ZFNs have diverse applications, from treating genetic disorders to advancing agricultural practices. The success of the Human Genome Project has been instrumental in providing the genetic blueprint necessary for these innovations.