CRISPR stands for clustered regularly interspaced short palindromic repeats.’ The term references a series of repetitive patterns in the DNA of bacteria discovered in the 90s. 20 years later, Jennifer Doudna and Emmanuelle Charpentier discovered that CRISPR-Cas9 could be used to cut any desired DNA sequence by just providing it with the right template, meaning it could be used as a gene-editing tool. To add a desired DNA sequence, one needs an upgraded version of CRISPR editing called CAST, CRISPR-associated transposases. Unfortunately,  CASTs suboptimally insert more DNA sequences than wanted and have a relatively high rate of unwanted off-target integration at unintended sites in the genome. This leads to mutations, the three being, silent mutations, missense mutations, and nonsense mutations. A silent mutation is an insertion or deletion of a nucleotide that doesn’t change the amino acid sequence. A missense mutation is an insertion or deletion of a nucleotide that changes one or more of the amino acids. Lastly, a nonsense mutation leads to an early stop signal.

4.2. The CRISPR Cas 9 system II

Luckily, new research published in Nature Biotechnology tells the reader that an improved CAST system called HELIX now exists. Helix stands for Homing Endonuclease-assisted Large-sequence Integrating CAST-compleX. This mouthful dramatically increased the efficiency of correct DNA insertions, reducing insertions at unwanted off-target sites. HELIX has over a 46% increase in on-target integration compared to that of the CAST system. This discovery is one of many that will continue to help us understand the complexity of our genes.

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