15.1: What is Genetic Engineering?
Genetic engineering is the process of modifying an organism’s DNA to introduce new, desirable traits. Many organisms, from bacteria to plants and animals, have been genetically modified for academic, medical, agricultural, and industrial purposes. While genetic engineering has definite benefits, ethical concerns surround modifying humans and our food supply.
Scientists can Deliberately Modify an Organism’s Genome
Genetic engineering is possible because the genetic code—the way information is encoded by DNA—and the structure of DNA are universal among all life forms. As a result, an organism’s genetic code may be modified in several ways.
The nucleotide sequence may be selectively edited by using techniques such as the CRISPR/Cas9 system. Known as the "molecular scissors," the CRISPR/Cas9 system is an innate, prokaryotic immune response that has been co-opted for editing genetic information.
A gene may also be removed from an organism to create a “knockout,” or introduced to create a “knockin,” through a process called gene targeting. This method relies on homologous recombination—genetic exchange between DNA molecules that share an extended region with similar sequences—to modify an endogenous gene.
Scientists can also insert a gene from one organism into the genome of another, resulting in a transgenic organism. Generally, DNA combined from different sources is called recombinant DNA. The organism that receives that DNA is considered a genetically modified organism or GMO.
Genetic Engineering Impacts Human Health and Well-Being
Genome editing has significantly impacted scientific research, agriculture, industry, and medicine. Molecular biology research often inserts transgenes—foreign genes—into bacteria and viruses to study gene function and expression. Bacteria were the first organisms to be genetically engineered. Scientists introduced the human insulin gene to produce synthetic insulin that is used by people with diabetes.
A technique called gene therapy allows a new gene to be inserted into a person so that the protein it encodes can be expressed within their cells. Gene therapy provides a cure or treatment for some serious and otherwise untreatable genetic diseases. Scientists modified viruses to deliver new genes to host cells. These customized viruses can infect diseased cells and insert a correct copy of a defective gene, treating human disorders such as Severe Combined Immunodeficiency (SCID).
Although many gene therapy treatments use modified viruses, the CRISPR/Cas9 system has become an increasingly popular technique. The CRISPR/Cas9 system cuts DNA by using a guide—RNA sequences known as CRISPR—to direct the “molecular scissors”—an enzyme called Cas9—to specific sites in the genome. Scientists use this molecular tool to add, remove, or alter genetic material. CRISPR/Cas9 has been used in mouse models to correct errors in genes that are responsible for Duchenne muscular dystrophy, Hepatitis B, cataracts, and cardiovascular disease.
While genetic engineering can yield new treatments for diseases, it can also be used for other practical purposes. Transgenic goats have been developed that produce spider silk in their milk for industrial use. In agriculture, some plants have been genetically modified to improve characteristics such as nutritional content and pest resistance. Recent and future advances in genetic engineering will likely continue to impact both human health and well-being.
Ethical Concerns Regarding Genetic Engineering
Genetic engineering has great potential, but where do we draw the line? Scientists and society must answer this question. Human genome editing, especially in germline cells, is a major ethical concern. Most gene therapies modify somatic cells, so genetic changes only affect the individual. Changes to a person’s germline, however, are also inherited by their offspring.
In 2018, a scientist shocked the world when he allegedly created the first babies genetically modified with CRISPR. He attempted to make the twin baby girls resistant to HIV by introducing an unstudied germline mutation. His actions sparked outrage and concern as scientists and the public grappled with what this meant for humankind. It remains unclear how this will affect the girls’ health, their future offspring, or the population.
Another concern is the use of foreign genetic material to improve the food supply. Plants are the most common genetically modified food source, with 28 countries growing nearly 450 million acres of GM crops globally. While there is enormous potential to secure food supply for a growing world population, scientifically sound, long-term studies are needed to address the concerns of GMO critics.