The polymerase chain reaction (PCR) is used to make millions of copies of a target piece of DNA. It is an indispensable tool in modern molecular biology and has transformed scientific research and diagnostic medicine.
The Human Genome Project was one of the main drivers that contributed to the development of PCR technology, and it has allowed us to identify many genes related to certain phenotypes, including genetic disorders.
Genetic disorders are caused by mutations that range from simple changes in the base sequence of the DNA double helix through to changes in large DNA sequences and even whole chromosomes.
PCR helps focus on the actual segment of DNA that is of interest, rather than the whole genome. From a small genetic sample, the genotypes can now be determined, and as a result, many genetic disorders can be detected, diagnosed and monitored. In some cases, gene therapy is available to address these disorders, and PCR is used to monitor the functioning of the relevant genes and gene segments.
Genotyping is also used for sex determination of embryos as well as detecting chromosomal and genetic disorders in the foetus.
The availability of personal genome testing – determining an individual’s unique genetic sequence – has also led to the growth of an industry in personalised medicine. Nutrigenomics is a specific form of consumer genomics, linking genetic information to information about foods that might be better or worse for particular conditions, like inflammatory bowel disease.
You might be interested to read these articles on the Science Learning Hub: Studying genetic diseases: Finding out about the genes, Designer babies – fact or fiction?, A genetic test for lactose intolerance, The human genome – now done in a day, DNA sequencing and genetic diseases and Biotech therapies.
Pathogenic microorganisms, including some viruses, bacteria, parasites and fungi, cause infectious diseases and can be identified using PCR, aiding efficient diagnosis and treatment. There are various articles on the Science Learning Hub exploring these techniques including Techniques for pathogen testing, Testing for Legionnaires’ disease, Tracing zoonoses and Virus hunters.
PCR is also used in molecular diagnostics and biochemical analyses. Among other things, these techniques can be used in drug development, especially in measuring the efficacy of drug therapy and research into cancer detection and treatment. Some related media and articles on the Science Learning Hub include Improving enzymes to help fight cancer, Pig viruses and virus testing, Melanoma risk gene identified and Mutating genes to detect cancer.
Technologies designed to create new products that meet specific human health needs also often rely on PCR as part of the process.
For example, some medicinal products are produced by genetic modification (GM) of existing organisms. This includes GM microorganisms to mass produce pharmaceuticals such as insulin and some antibiotics. Check out Bacterial libraries for improving proteins and Directed evolution for more information.
Sometimes, genetic modification involves transfer of genes from one organism to another – this is called transgenics. Although the applications of this are relatively new to medicine, this is a growing field of research. For further reading about transgenics research in New Zealand, see Transgenic cows – introduction.
Transplant technologies can also use PCR to improve the accuracy of tissue typing, thereby reducing the likelihood of transplant rejection. Transgenic animals are also bred for the purpose of xenotransplantation. Pigs are commonly used for this purpose. Read more in these articles: Pig cell transplants – introduction, Pig cell to human brain transplant approved and Trialling pig cell transplants.
There is potentially a huge amount of genetic information provided by modern genetic technologies.
- What are some of the ethical considerations regarding the use of this information?
- What sorts of choices become available to people due to having this information?
- What ethical considerations might there be in using this information?
- If you had your genome mapped, who do you think should be able to have access to your information?
Nature of science
The Hub has a number of resources on PCR, including, What is PCR?, PCR in action: Adding genes to cells and Using gel electrophoresis to check a PCR reaction. There are also many useful applications of PCR technology – see What is PCR used for? to find out more.
In the activity How does PCR work?, students are asked to view a video and conduct their own research in order to develop an understanding of the polymerase chain reaction process and why it is important.