Genetic and genome engineering is a useful tool for researchers, from producing proteins to understanding disease, and the polymerase chain reaction (PCR) has a vital role supporting this process by cloning the DNA fragments used to modify the genomes of the bacteria, yeasts, animals and plants used in biological, agricultural and medical research.
PCR is used to created millions or billions of copies of DNA through repeated cycles of denaturing, which separates the DNA into its two strands; annealing, which attaches specific primers that mark the beginning and end of the DNA to be copied; and extension/elongation, where the DNA strands are used as templates to build two new strands of DNA (see PCR 101: An introduction to PCR for more details). These cloned DNA fragments can then be inserted into the target organism, including microorganisms, plants or animals, using vectors such as bacteria and viruses. Some of these traits can be passed on to the next generation.
The bacterium Escherichia coli was the first organism to be genetically engineered, in the 1970s. Bacteria have simple genetics and a short lifecycle, so the results of genetic manipulation can be seen quickly. The simplest form of genetic engineering in E coli is knocking out genes to look at the impact on development.
Researchers can genetically engineer plants (and other organisms) to knock out or overexpress genes to learn about their function and impact on development, health and disease.
Fruit flies (Drosophila) are commonly genetically engineered, and transgenic fruit flies are widely used in research to learn more about monitor genetic development and see the effect of changes and mutations. Fruit flies are poplar in research because they have small genomes, are easy to handle, and have a relatively short lifecycle.
Zebrafish (Danio rerio) and medaka (Oryzias latipes) are often used in developmental biology and genetic research. They have embryos made up of one cell that is relatively easy to inject with the target DNA and their development is rapid. Genetically-modified zebrafish have also been used to detect pollution in waterways.
Transgenic animal models, such as mice and rats, can mimic human diseases, to test potential drugs before moving into clinical trials.
Transgenic animals can be used to understand the causes and pathways of disease – for example, engineering animals to express green fluorescent protein (GFP) helps track the efficacy of gene therapies or understand more about viral infection.
Transgenic animals can be used to produce proteins or tissues used to treat human disease.
PCR can also be used to detect the presence and quantity of known genetically modified organisms (GMOs) in the environment, by detecting the sections of DNA that are known to be modified. The technique can also be used to find unknown GMOs by targeting sequences that are common to many genetic modifications, such as the 35S transcription promoters or the stop signal known as the NOS terminator.