CIE A Level Biology (9700) exams from 2022

Revision Notes

19.1.7 Gene Editing

Gene Editing

  • Gene genome editing (or 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 is a form of genetic engineering where foreign DNA is not introduced into the genome
  • Gene editing enables the scientists to be more accurate in their manipulation of the genome. In the past, inaccurate methods using vectors were used. These included:
    • Modifying viruses to insert DNA into the gene causing the disease. However this resulted in DNA being inserted into other genes causing unforeseen consequences
    • Liposomes (small spheres of lipid molecules) containing the normal gene which was 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 the ‘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 are 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

Author: Catherine

Cate has over 20 years’ experience teaching Biology to IGCSE, IB and A-level students in seven different countries across Asia, Europe, North America and the Middle East. This has given her a fine appreciation of different cultures, places and teaching methods. Cate has a keen interest in producing Biology revision resources that will help students engage with the subject.
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