There are many technologies used to edit the genetic makeup or genome. CRISPR or ‘Clustered Regularly Interspaced Palindromic Repeats’ is the latest technique of gene-editing (Redman et al., 2016).
What role does Cas9 play in the CRISPR process?
Cas9 is an endonuclease that produces a break in both strands of the DNA (Redman et al., 2016). When the DNA breaks from a specific site, modifications can be made to it. Cas9 proteins occur naturally in bacteria and provide them protection against viruses
How does the CRISPR-Cas9 system snip and replace any DNA sequence?
Two essential components constitute the CRISPR/Cas9 system; an RNA guide to locating the target gene that needs to be snipped and an endonuclease (CRISPR-associated protein Cas9) that breaks the DNA at the site of the gene removal (Redman et al., 2016). The RNA guides the Cas9 to the site of cleavage. sgRNA or synthetic single-guide RNA is an 18-20 nucleotide segment of the RNA that binds to the DNA. The protospacer adjacent motif (PAM) is a 2-5 nucleotide DNA sequence that lies at the 3’ end of the sgRNA and specifies the site of DNA cleavage. After the double-strand break (DSB) is produced, DNA repair occurs through two mechanisms; homology-directed repair (HDR) or non-homologous end joining (NHEJ). HDR is the method used for precise editing of genes through the CRISPR/Cas9 system in which the DNA template is a piece of homologous DNA.
Benefits and Drawbacks of Gene Editing
Gene editing can be used to modify the DNA of plants, animals, and humans.
Genetically Modified Plants
The benefits and disadvantages of modifying plants through gene editing are (Phillips, 2008);
Plants can be genetically modified in such a way to make them more resilient and resistant to diseases and pest attacks. Pest resistance in crops will lead to lower use of pesticides. High-yield, fast-maturing, and nutrient-rich crops can be created to prevent famine and cater to the growing world population. It can also reduce costs associated with crop production. For example, plants resistant to an insect, the European corn borer can be created through the expression of Cry1Ab; an insecticidal protein.
The long-term effects of GM plants on human health are unknown. In addition to unknown effects on humans, there can be possible environmental effects. New allergens can arise. Antibiotic resistance, herbicide, and pesticide effect of crops can be transmitted horizontally to humans. Vertical gene transfer can occur between modified crops and natural wild counterparts.
Genetically Modified Animals
Genetically modifying organisms has the following benefits and disadvantages (Perzigian, 2003)
Gene editing can help to eliminate certain diseases from animals even before the birth of the animal. Animals can be modified to be more productive e.g., to produce more milk, more meat, more wool. Their growth rates can be modified to enable them to mature faster. This can also have economic benefits for the food and agricultural industry. The animals can be modified to produce drugs and proteins in their milk, reducing the cost of production of these substances.
The animals can be exploited only for their beneficial purposes. It can impact the diversity of animals and the process of natural selection. It also affects the rights of an organism to be free from genetic modification. Cloning near-extinct animals can divert the limited resources required to sustain and protect the life and habitat of these animals.
Genetic Modification of Humans
In humans, gene editing can serve as a cure for certain diseases like cystic fibrosis (Niglia, 2021). Cancer immunotherapy can also utilize gene editing by modifying T cells. Diseases affecting the human lifespan, like diabetes may not be treated by using genetic engineering resulting in a prolonged lifespan. Germ-line can be modified to prevent diseases to be transmitted from parents to children. Genes for intelligence, strength, physical features can be introduced to produce humans with superior physical and mental capabilities.
As the long-term effects of genetic modification and germline editing are unknown, performing these procedures without enough trials can lead to a safety concern for the modified organisms (Niglia, 2021). New diseases may arise as a result of gene modification. A child conceived after germ-line modification can cause pregnancy complications like premature birth, miscarriage, and stillbirth. The cost of these techniques is very high so not everyone may have access to these advancements. Off-target modifications can occur.
Risk vs reward of modifying animal DNA?
Several gene-editing tools are used. Each has its benefits and disadvantages.
Ethical Issues of Gene Editing
Most ethical issues arise from the editing of germ-line (Ayanoğlu et al., 2020). These include the issue of consent from an unborn offspring. The creation of designer babies. The inequitable access of these procedures between the rich and poor. The cloning of humans to harvest organs is also an ethical issue pertinent to genetic modification.