Introduction:CRISPR, a recent breakthrough in genetic engineering, has been widely considered a life-changing discovery. It is a new technology that allows scientists to edit the DNA of humans. CRISPR stands for: clustered, regularly interspaced, short, palindromic repeats. CRISPR is considered to have the potential to eradicate viruses such as HIV (Le Page, 2015.) Yet do these incredible breakthroughs come without cost? What is CRISPR?CRISPR cas9 is a gene editing technique. The technique offers the potential to change any sequence of DNA, the ability to turn genes off, one at a time and to see what they do (Le Page, 2015.) CRISPR is an acronym for: Clustered, regularly interspaced, short, palindromic repeats. CRISPR cas9 contains spacers and nucleotide repeats. A protein called cas9 cuts a sequence from DNA. The protein is attached to an RNA sequence identical to the target sequence in the DNA that the scientist wants to edit. CRISPR cas9 is able to alter any DNA sequence through altering the RNA/cas9 complex to recognise the target sequence. The cas9 RNA complex is placed inside the cell, the cas9 protein is able to find the target sequence of DNA, a chemical reaction will take place which cuts the sequence in the correct place (Jinek et al., 2012.) Once the removal of the target DNA has taken place the cell’s repair mechanism operates. In order to join the two ends of DNA there are two possible methods the cell carries out. The first method known as: ‘non-homologous end joining,’ occurs when the two cuts of the DNA are joined. However, mutations may occur through this method as nucleotides have the potential to be deleted or inserted by the cell. The second method offers scientists increased control, it allows the further altering of a gene through supplying a DNA template which is inserted into the gap (Vidyasagar, 2017.) This alters the mutation within the sequence as the correct one has been added. History of CRISPRCRISPR cas9 was originally used to enhance the defence system of bacteria and archaea. CRISPR cas9 was a tool used to prevent attacks from viruses and other invaders, this was achieved through the destruction of the viral DNA (Barrangou et al., 2007.) The first experimental use of this method was carried out by Rodolphe Barrangou and his team in 2007, using the bacteria Streptococcus thermophilus. Barrangou altered bacterial immunity through removing and adding spacers into both the virus and bacteria (Deveau et al., 2007.) However, CRISPR has been enhanced from previously existing gene editing techniques such as: Transcription Activator-Like Effector Nucleases (TALEN) and Zinc Finger Nucleases (ZFNs.) ZFNs are based on a Fokl restriction enzyme fused to a zinc finger. The zinc finger fuses with a nucleotide triplet. TALENS are naturally occurring proteins formed from the bacteria Xanthomonas. ZFNs and TALEN both work through Fokl. Combining different TALENs allows a specific sequence within DNA to be targeted (Gaj, Gersbach and Barbas, 2013.) ZFNs and TALEN, although effective, have been enhanced into a cheaper, more efficient method: CRISPR. Current use of CRISPR and the futureScientists hope CRISPR can contribute to a number of things from the treatment of HIV to the ability to design embryos with the most desirable features. 2. Two examples of the current use of CRISPRHuman immunodeficiency virus Researchers from Temple University and Pittsburgh University in the US managed to eliminate HIV from mice using CRISPR (Yin et al., 2017.) CRISPR cas9 was programmed to target the viral DNA and remove it. However, problems appeared due to the nature of the virus. Small mutations caused changes in the sequence of the viral DNA resulting in the cas9 being unable to recognise and target it. Viral DNA may escape the cas9 protein and become increasingly more difficult to target in the future, this results in unexpected resistance. The treatment of Human immunodeficiency virus (HIV) is one of great global importance. HIV infects the CD4 cells within the body, these cells replicate thousands of times. CD4 cells defend the body and are part of the immune system, HIV is so deadly as it reduces the number of CD4 cells over time, weakening the body’s immune system. According to the World Health Organisation and the Joint United Nations Programme on HIV/AIDS at the end of 1999, an estimated 34.3 million people were living with HIV/AIDS. It is predicted that HIV will be responsible for 40% of deaths caused by infectious disease by 2020 (Gayle et al., 2001.) CRISPR has the potential to be used in the treatment of HIV. Dr. Chen Liang, Senior Investigator at the Lady Davis Institute at the Jewish General Hospital and the Associate Professor of Medicine at the McGill University AIDS Centre believes that despite the current limitations of CRISPR, it could ultimately be successfully used in the future (Genomics Research from Technology Networks, 2016.)Engineering of human embryosOn the 1st of February 2016 a team of scientists at the Francis Crick Institute in London were permitted by the UK Human Fertilisation and Embryology Authority (HFEA) to use CRISPR/cas9 on embryos (Callaway, 2017.) This was the first time such research had been permitted anywhere in the world. The research aims to improve treatments for infertility amongst women. Genetic engineering (the deliberate modification of the characteristics of an organism by manipulating its genetic material (Oxford Dictionaries | English, n.d.)) has always sparked debate. Particularly in this case, as the researchers plan to use healthy embryos, genetically modify them and then destroy them within 7 days. However, the project aims to increase pregnancy rates, which would ultimately bring more life into the world than take it away. The Francis Crick Institute’s research was soon followed by a different group of scientists, led by Junjiu Huang at Sun Yat-sen University in Guangzhou, China, they conducted similar research to the scientists at the Crick Institute (Liang et al., 2015.) However, the embryos used were non-viable which would not be able to develop into a foetus, which is considered more ethically acceptable. The genetic modification of embryos was beginning to gain speed due to factors such as the use of non viable embryos. This suggests that genetic engineering can be achieved without causing unnecessary controversy which potentially prevents such research from taking place. The future of CRISPR/cas9CRISPRs’ full potential lies in the editing of embryos. Embryonic editing can make significant changes not only for the child but for the next generations. Scientists are working on this area due to the sheer impact these small changes have on society and the gene pool. However, CRISPR is still under trial and requires extensive modification in order to cure some of medicines big problems. However, CRISPR cas9 in theory can cure any single-gene disease. Diseases such as Huntington’s disease, sickle cell and cystic fibrosis may, in the future, no longer be a problem. Single-gene diseases have straight forward inheritance patterns, they are either recessive or dominant, a recessive gene is only the phenotype (physically visible) if both parents have it (Alliance, 2010.) Dominant genes are always the phenotype without both parents needing to be carrying it. The recessive or dominant nature of such diseases are so significant as it means these diseases affect millions of people. A parent with a dominant allele of the disease is guaranteed to pass on that specific disease to their offspring and future generations. Engineering the single-gene that causes a particular gene is a start to changing the health of generations.