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Crisper - Cas 9 - the Strengths and Weaknesses of This Remarkable Technology

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“Many genetic disorders result from a gene mutation that is present in essentially every cell in the body” (“How Are Genetic Conditions Treated or Managed? - Genetics Home Reference - NIH.”). As a result, these disorders often affect many body systems including: blood cells, the immune system, and hearing. Most cannot be cured by conventional means: Cystic Fibrosis and Huntington's disease are examples which still have no cure.

In recent years, scientific research has found a possible solution. The answer may be found in Clustered Regularly Interspaced Short Palindromic Repeats, which are the “hallmark of a bacterial defense system that forms the basis for CRISPR” (“Questions and Answers about CRISPR.”) CRISPR was first discovered in the late 1980s as unidentified repeating segments of DNA in the E. coli bacteria genome. The functions of these segments were unknown until the early 2000s, where a “Spanish researcher recognized that the E. coli genome was exceptionally similar to viral DNA. CRISPR is theorized to help remember past viral infections by recording them in the bacterial cell's DNA,” (Lasker Foundation). This would be proven later in 2012 when scientists realized that it is possible to program CRISPR to detect select segments of genes. This was a breakthrough in medical science because humans now had the capability to edit genes. The idea of curing cancer and genetic diseases now didn’t seem impossible. However, CRISPR can only detect and recognize the programmed gene sequence; it can’t repair or remove that damaged gene. For this, an enzyme was needed. Cas9 or "CRISPR-associated 9" is an enzyme that requires the CRISPR sequence as a map to identify and the separate specific strands of DNA. CRISPR cannot perform without Cas9 and vice versa. Together, they form CRISPR-Cas9, a genome editing technology that gives humans the ability to change an organism's DNA. The way that it works can be explained quite simply.

CRISPR-Cas9 is a technology which allows medical researchers, scientists, geneticists and to edit a person’s genome by removing, or adding segments of their DNA sequence. For CRISPR to identify genes that are unwanted in humans, it first has to be programmed with the genetic sequence of the targeted gene that is causing the disease. The CRISPR sequence leading the Cas9 enzyme is then capable of guiding Cas9 to a matching series of DNA. While inside the cell nucleus, the CRISPR-Cas9 system flows closely along the genome, bonding itself every time a sequence called PAM is discovered. Pam, or “Protospacer adjacent motif” consists of just several base pairs, but Cas9 needs it to grab onto the DNA. By grabbing it, the protein is able to destabilize the neighboring sequence, opening a thin gap in of the double helix shape of the DNA, allowing CRISPR to clearly detect whether if the DNA identified matches the targeted gene. If not, they move on to the next. But if the recognized DNA sequence matches, Cas9 binds to the DNA to produce two pincer-like appendages, which cut the targeted gene in two. This targeted gene could be causing cancer, this gene could also be the reason for a genetic disease the person may have. Besides Cas9, there are also other enzymes that use CRISPR as a guide for their own purposes. For example, Cas3, which consumes DNA like a white blood cell, or Cas13; which is used to “develop sensitive tests for viral infections”(Molteni, Megan). Right now, scientists are still working trying to add more improvements to CRISPR, but Cas9 is currently the most widely used. Removing and destroying a bad or damaged gene could end there, but there is also the possibility to add healthy DNA. This discovery has the potential to be used in many ways.

CRISPR could cure all genetic diseases and because it is affordable and easy to produce, it has potential application beyond humans, to help with pest control and agriculture. CRISPR does not rely on DNA recognition, but ribonucleotide complex formation. This way CRISPR can be designed, prepared, stored and sold cheaply, like a vaccine to target any sequence in the genome. CRISPR may not just allow us to cure all genetic diseases, but it may change the world and how we view disease. “Agricultural companies are interested in the technology's potential” (Lasker Foundation) to genetically edit crops to make them create their own herbicide, grow faster, and to produce larger fruit. Farmers have also shown interest in terms of hog farming. Porcine Reproductive and Respiratory Syndrome Virus, or Pig Flu, is capable of being transmitted to any hoofed farm animal. Once the contagious disease is in a pen, there isn't much the farmer can do to reduce the spread. This disease causes so many miscarriages and deaths across farms around the world, that it costs just the US economy alone around $600 million dollars a year.“Scientists have also begun to explore how CRISPR can alter populations of mosquitoes to prevent transmission of Zika virus or malaria.” (Lasker Foundation). All of these applications lead scientists to be very optimistic about its use, but there is always the chance for associated problems.

Although CRISPR could be extremely useful in curing genetic diseases by simply removing the bad gene, there are potential



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