You have probably heard of GMOs, but do you know what they are exactly? They're increasingly all around us, in our food and agriculture, our ecosystems, and even our medicine. How about genetic modifications in general? Our ability to manipulate our and every being's DNA, from reading to writing and editing, is changing the world around us and ushering in a new bioengineering age! What will we do with this power?
We'll learn about the types of genetic modification that exist, examples of their uses, the difference with genetic engineering, and their pros and cons.
Genetic modification definition
All organisms have a genetic instruction code that determines their characteristics and behaviour. This DNA instruction is called the genome, it consists of hundreds to thousands of genes. A gene can encode the sequence of amino acids in a polypeptide chain (protein) or a non-coding RNA molecule.
The process of modifying an organism's genome is known as genetic modification, and it is often done with the aim of modifying or introducing a particular trait or multiple traits in the organism.
3 types of genetic modification
Genetic modification is an umbrella term that includes various types of making alterations to an organism's genome. Overall, genetic modification can be categorized into three main types: selecting breeding, genetic engineering, and genome editing.
Selective breeding
Selective breeding of organisms is the oldest type of genetic modification that has been done by humans since ancient types.
Selective breeding describes the process by which humans selectively choose which males and females would sexually reproduce, with the aim of enhancing specific features in their offspring. Various species of animals and plants have been subject to continuous selective breeding by humans.
When selective breeding is done over multiple generations, it can result in significant changes in the species. Dogs, for instance, were probably the first animals to be intentionally modified by selecting breeding.
About 32,000 years ago, our ancestors domesticated and bred wild wolves to have enhanced docility. Even in the last few centuries, dogs have been bred by people to have desired behaviour and physical features that have led to the wide variety of dogs present today.
Wheat and corn are two of the main genetically modified crops by humans. Wheat grasses were selectively bred by ancient farmers to produce more favourable varieties with larger grains and hardier seeds. Selectively breeding of wheat is carried on to this day and has resulted in the many varieties that are cultivated today. Corn is another example that has seen significant changes over the last thousands of years. The early corn plants were wild grasses with tiny ears and very few kernels. Nowadays, selective breeding has resulted in corn crops that have large ears and hundreds to a thousand kernels per cob.
Genetic engineering
Genetic engineering builds upon selective breeding to reinforce desirable phenotypical characteristics. But instead of breeding organisms and hoping for the desired outcome, genetic engineering takes genetic modification to another level by directly introducing a piece of DNA into the genome. There are a variety of methods used to perform genetic engineering, most of which involve the use of recombinant DNA technology.
Recombinant DNA technology includes manipulating and isolating DNA segments of interest using enzymes and different laboratory techniques.
Typically, genetic engineering entails taking a gene from one organism, known as the donor, and transferring it to another, known as the recipient. Since the recipient organism would then possess foreign genetic material, it is also called a transgenic organism.
Transgenic organisms or cells are those whose genomes have been altered by the insertion of one or more foreign DNA sequences from another organism.
Genetically engineered organisms often serve one of two purposes:
Genetically engineered bacteria can be used to produce large quantities of a particular protein. For example, scientists have been able to insert the gene for insulin, an important hormone for the regulation of blood sugar levels, into bacteria. By expressing the insulin gene, the bacteria produce large volumes of this protein, which then can be extracted and purified.
A particular gene from a donor organism can be introduced into the recipient organism to introduce a new desired trait. For example, a gene from a microorganism that codes for a toxic chemical can be inserted into cotton plants to make them resistant to pests and insects.
The process of genetic engineering
The process of genetically modofying an organism or cell consists of many fundamental steps, each of which can be accomplished in a variety of ways. These steps are:
Selection of a target gene: First step in genetic engineering is to idenify which gene they want to introduce into the recipient organism. This depends on whether the desired characteristic is only controlled by a single or multiple genes.
Gene extraction and isolation: The genetic material of the donor organism needs to be extracted. This is done by restriction enzymes which cut out the desired gene out of the donor's genome, and leave short sections of unpaired bases on its ends (sticky ends).
Manipulating the selected gene: Following extraction of the desired gene from the donor organism, the gene needs to be modified so that it can be expressed by the recipient organism. For example, eukaryotic and prokaryotic expression systems require different regulatory regions in the gene. So the regulatory regions need to be adjusted before inserting a prokaryotic gene into a eukaryotic organism, and vice verse.
Gene insertion: After manipulation of the gene, we can insert it into our donor organism. But first, the recipient DNA would need to be cut by the same restriction enzyme. This would result in corresponding sticky ends on the recipient DNA that makes the fusion with the foreign DNA easier. DNA ligase would then catalyse formation of covalent bonds between the gene and the recipient DNA, turning them into a continous DNA molecule.
Bacteria are ideal recipient organisms in genetic engineering since there are no ethical concerns around modifying bacteria and they have extrachromosomal plasmid DNA that are relatively easy to extract and manipulate. Furtheremore, the genetic code is univeral meaning that all organisms, including bacteria, tranaslate the genetic code into proteins using the same language. So the gene product in bacteria is the same as in eukaryotic cells.
Genome editing
You can think of genome editing as a more precise version of genetic engineering.
Genome editing or gene editing refers to a set of technologies that allow scientists to modify an organism's DNA by inserting, removing, or changing base sequences at specific sites in the genome.
One of the most well-known technologies used in genome editing is a system called CRISPR-Cas9, which stands for 'Clustered regularly interspaced short palindromic repeats' and 'CRISPR associated protein 9', respectively. The CRISPR-Cas9 system is a natural defensive mechanism used by bacteria to fight against viral infections. For instance, some strains of E. coli ward off viruses by cutting and inserting sequences of the viral genomes into their chromosomes. This will allow the bacteria to 'remember' the viruses so, in the future, they can be identified and destroyed.
Genetic modification vs genetic engineering
As we just described, genetic modification is not the same as genetic engineering. Genetic modification is a much broader term that genetic engineering is only a subcategory of. Nevertheless, in the labelling of genetically modified or GMO foods, the terms 'modified' and 'engineered' are frequently used interchangeably. GMO stands for genetically modified organism in the context of biotechnology, however, in the field of food and agriculture, GMO only refers to food that has been genetically engineered and not selectively bred.
Uses and examples of genetic modification
Let's have a closer look at a few examples of genetic modification.
Medicine
Diabetes mellitus (DM) is a medical condition in which the regulation of blood glucose levels is disrupted. There are two types of DM, type 1 and type 2. In type 1 DM, the body's immune system attacks and destroys the cells that produce insulin, the main hormone for lowering blood glucose levels. This results in elevated blood sugar levels. Treatment of type 1 DM is by injection of insulin. Genetically engineered bacterial cells that contain the human gene for insulin are used to produce insulin in large quantities.
Fig. 1 - Bacterial cells are genetically engineered to produce human insulin.
In the future, scientists will be able to use gene editing technologies such as CRISPR-Cas9 to cure and treat genetic conditions such as combined immunodeficiency syndrome, cystic fibrosis, and Huntington's disease by editing the faulty genes.
Agriculture
Common genetically modified crops include plants that have transformed with genes for insect resistance or herbicide resistance, resulting in higher yields. Herbicide-resistant crops may tolerate the herbicide while the weeds are being killed, using less herbicide overall.
Golden rice is another GMO example. Scientists inserted a gene into wild rice that enables it to synthesize beta-carotene, which after being eaten is converted to vitamin A in our body, a vital vitamin for normal vision. The golden colour of this rice is also because of the presence of beta-carotene. Golden rice can be used in deprived locations where vitamin A deficiency is common to help improve people's eyesight. Many countries, however, have prohibited the commercial cultivation of golden rice due to concerns about the safety of GMOs.
Genetic modification pros and cons
While genetic modification comes with many advantages, it also carries some concerns about its potential adverse effects.
Advantages of genetic modifications
Genetic engineering is being used for producing medicines such as insulin.
Gene editing has the potential to cure monogenic disorders such as cystic fibrosis, Huntington's disease, and combined immunodeficiency (CID) syndrome.
GMO foods have a longer shelf life, more nutrient content, and higher production yield.
GMO food containing essential vitamins can be used in deprived areas to prevent diseases.
Gene editing and genetic engineering in the future can potentially be used to enhance life expectancy.
Disadvantages of genetic modifications
Genetic modifications are fairly new, and hence we are not fully aware of what consequences they might have on the environment. This raises a few ethical concerns that can be categorized into the following groups:Potential environmental damage, such as increased prevalence of drug-resistant insects, pests, and bacteria.
Potential harm to human health
Detrimental influence on conventional farming
GM crop seeds are often significantly more expensive than organic ones. This can lead to excessive corporate control.
Genetic Modification - Key takeaways
- The process of modifying an organism's genome is known as genetic modification.
- Genetic modification is an umbrella term that includes various types:
- Selective breeding
- Genetic engineering
- Gene editing
- Genetic modifications have various medical and agricultural applications.
- Despite its many advantages, genetic modification carries ethical concerns about its potential consequences on the environment and adverse effects on humans.
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