Gene Editing (HL) (HL IB Biology)

• The entire set of genetic material of an organism is known as its genome
• Biologists now know the entire human genome (they have worked out all the genes that are found in humans)
• The Human Genome Project (completed in 2003) was the name of the international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings
• This was a very important breakthrough but following this scientists now want to know what each gene codes for and the effect of a gene on an organism; this will help us better treat and prevent disease

Gene knockout

• One way to find out the effect and function of a gene on an organism is to remove it from the genome or make the gene unusable; this technique is called gene knockout
• The organism that has had its genes "knocked out" is called a knockout organism
  • Common knockout organisms are laboratory mice
• Scientists create knockout organisms to study the impact of removing a gene from an organism, which often allows them to then learn something about that gene's function
• This is classed as a genetic engineering technique
• A genetic library of knockout organisms exists, such as for the bacterial species Saccharomyces cerevisiae, exists in order to
  • Understand the mechanism of action of a drug
  • Target specific biological processes or deficiencies
• Conditions that have been studied using gene knockout techniques include
  • Obesity
  • Diabetes
  • Cancer likelihood
  • Addiction
  • Cardiovascular disease

• Gene, or genome, editing allows genetic engineers to alter the DNA of organisms by inserting, deleting or replacing DNA at specific sites in the genome known to cause disease.
  • It differs from genetic engineering in that it involves modification of the existing DNA of an organism rather than the insertion of DNA from another organism.
  • Note that the term 'genome' refers to all of the DNA, or genetic information, found inside a cell.
• Gene editing enables the scientists to be more accurate in their manipulation of the genome
• Older gene editing techniques include
  • Modifying viruses to insert DNA, e.g. into the gene causing a disease
    • This sometimes resulted in DNA being inserted into other genes causing unforeseen consequences
  • Liposomes (small spheres of lipid molecules) containing the normal version of a gene being sprayed into noses
    • This was only a short-term solution as the epithelial cells lining the nasal passageway were short lived
• Today scientists have developed new gene editing techniques, the most commonly used one being CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)
  • This technique involves using the natural defense mechanism bacteria (and some archaea) have evolved to cut the DNA strands at a specific point as determined by a guide RNA attached to an enzyme (Cas9)
  • Once cut scientists can then either insert, delete or replace faulty DNA with normal DNA
• Gene editing is involved in gene therapies (e.g. developing treatments for cystic fibrosis and sickle cell anaemia).
  • Gene therapy is the treatment of a genetic disease by altering the person’s genotype
• As scientists learn more about the human genome (from the Human Genome Project) and the proteome, and have the technology to process large quantities of data through computational biology, they can gain a better understanding of which genes are responsible for genetic diseases and where they are located,and therefore what base changes need to occur to treat or cure the disease

Gene editing techniques diagram

CRISPR is an example of a gene editing technique

NOS: Certain potential uses of CRISPR raise ethical issues that must be addressed before implementation

• Genetic engineering practices raise a number of ethical issues that need to be considered
  • Issues may arise around consent of genetic data
  • Insurance companies may require data on genetic testing results
  • The need for legal control over how data is used, particular data involving human genomes
• Fortunately decisions based on the morality of genetic engineering tend to be made on a world wide scale 
• Ethics committees exist which must approve all experiments carried out  and they gain advice and guidance from world leading experts
• Countries have their own laws in place to protect participants of genetic technology research
• International committees have been formed to discuss and debate the issues raised and make recommendations to governments, scientists so that any policies made have considered the ethics involved
  • One such committee is The International Commission on the Clinical Use of Human Germline Genome Editing
• The World Health Organisation (WHO) plays an important role to create guidance for best practice and issue guidelines
• The challenge is to ensure that all policy makers and countries work together to coordinate regulations 
• These international regulations are applied to all gene editing processes including CRISPR