Table of ContentsSummaryGene DrivesProposed Gene Drive MethodsCRISPR/Cas9 and Gene DriveDangers and Precautionary MeasuresConclusionSummaryThis article reviews the overall process of gene drive and its methods. First, the reader will receive a brief overview of the concept of gene drives as well as a description of how gene drive systems can be used to manipulate Mendelian inheritance patterns. This article will focus on gene drive methods, the importance of CRISPR/Cas9, and the dangers of gene drives. Say no to plagiarism. Get a tailor-made essay on "Why violent video games should not be banned"?Get the original essayGene Drive Gene drive is a method by which geneticists seek to modify the normal patterns of Mendelian inheritance within a population. Gene drives work on Mendelian inheritance patterns via two different processes. In the first process, homing, a desired allele copies itself onto its homolog in place of the wild-type allele, leading to a higher number of offspring with that allele (Champer, Buchman & Akbari., 2016). . The second process works by reducing the viability of gametes containing wild-type alleles relative to gene drive alleles, thereby reducing the frequency of wild-type alleles in the population. The goal of gene drives, in general, is to either transmit a desired trait through a population (Modification) or to suppress/eliminate a population (Suppression) (Champer et al., 2016). Gene drives can achieve desired results through a number of different methodologies. Proposed Gene Drive MethodsA proposed method for gene drive seeks to mimic a natural process by which specialized genes seek out and target a gene on the opposite chromosome. The genes, endonuclease genes (HEG), encode a protein that binds to a specific sequence of nucleotides and cleaves DNA at that site. Gene drive systems based on this process are collectively known as homing-based drives (Champer et al., 2016). Naturally occurring HEGs cannot target specific genes. The task of identifying all possible natural HEGs and tailoring them to the individual needs of geneticists would be monumental. Instead, geneticists have turned to new technology enabling the creation of recombinant HEGs that can target any desired gene in a species' genome (Champer et al., 2016). This proposed method, CRISPR/Cas9, will be discussed later in this article. SEO-based drives work by forcing DNA repair through natural processes. The strand can repair itself without the help of a template strand by ligating the broken ends of the strand together, this pathway is known as non-homologous end joining or NHEJ (Gilles & Averof, 2015). If NHEJ occurs, the target gene will simply be excised and the strand will be repaired with the deleted gene. Repair can also occur through use of the template strand via homology-directed repair or HDR. In HDR, the HEG will serve as a template for repair of the targeted strand, resulting in the presence of the HEG in both homologous chromosomes (Champer et al., 2016). In either case, normal patterns of Mendelian inheritance will have been altered, due to the fact that homing-based drives operate during meiotic cell division (Champer et al., 2016). If NHEJ occurs, the target DNA will have reduced viability compared to HEG-containing DNA.Overall, this leads to a lower frequency of the wild-type allele, meaning that the HEG functions as a suppressive gene drive. HDR has the added benefit of propagating the mutant allele and reducing expression of the wild-type allele. Homing-based drives are desirable as a gene drive method due to this unique nature. Among the proposed gene drive methods, homing-based gene drive is the only method capable of both suppressing and modifying a population (Champer et al., 2016). Another proposed method of gene drive, sex-related meiotic drive aims to suppress a population by changing the number of male offspring to females. Sex-linked meiotic drives are similar to homing-based drives because they contain an endonuclease-carrying gene. This gene is linked to the sex of males of a species. In the presence of an X chromosome during meiotic division, the endonuclease produced by the target gene cleaves the X chromosome at several locations. Any X chromosome containing sperm will then be non-viable (Champer et al., 2016). Genes that act in this way are called X-shredder genes (Champer et al., 2016). Any offspring from males carrying the X-shredder genes will also be male. If the X-shredder genes are located on autosomal chromosomes, then it is possible for offspring to inherit X-shredder. If, on the other hand, the X-shredder gene is carried on the Y chromosome, then all the descendants of this male will carry the gene (Champer et al., 2016). Populations in which X-shredder alleles spread will see a large reduction in the number of female offspring. Eventually, the population will not be able to sustain itself, leading to successful suppression of the gene drive. Unfortunately, X-shredder genes do not exist for all species, geneticists hope to create recombinant X-shredder genes using the same method proposed for homing-based drives. The last proposed gene drive method, discussed in this article, is maternal dominant embryonic arrest (Medea). Medea occurs in females of a species during oogenesis (Champer et al., 2016). It was first identified in beetles. The mother insect carries a gene that expresses a toxin during oogenesis. Offspring who inherit the gene also inherit a gene that produces an antidote early in zygotic development. Zygotes that do not carry the Medea gene are unable to produce an antidote and die during development (Champer et al., 2016). Females carrying Medea select Medea carrying their offspring. The gene drives offered with Medea aim to exploit this process with recombinant DNA. By inserting the desired gene and creating a unique combination of toxin and antidote using CRISPR/Cas9 technology, geneticists will be able to rapidly spread a gene throughout a population. Of all the methods listed, natural processes have created the framework that geneticists seek to exploit. A logical improvement to any gene drive is the ability to target any gene as well as insert the desired gene into the genome of the target organism. This is exactly what the emergence of CRISPR/Cas9 technology promises. CRISPR/Cas9 and gene drives Clustered regularly interspaced short palindromic repeats (CRISPR) as well as CRISPR-associated protein 9 (Cas 9) are a gene drive endonuclease that allows geneticists to target any desired gene. thanks to the use of specialized guide RNAs (Gilles & Averof, 2015). An endonuclease is a protein that cleaves DNA. CRISPR is a system that bacteria.