Topic 19: Genetic Technology
19.1 Principles of genetic technology
​Students should be able to:
1) define the term recombinant DNA
2) explain that genetic engineering is the deliberate manipulation of genetic material to modify specific characteristics of an organism and that this may involve transferring a gene into an organism so that the gene is expressed
3) explain that genes to be transferred into an organism may be:
• extracted from the DNA of a donor organism
• synthesised from the mRNA of a donor organism
• synthesised chemically from nucleotides
4) explain the roles of restriction endonucleases, DNA ligase, plasmids, DNA polymerase and reverse transcriptase in the transfer of a gene into an organism
5) explain why a promoter may have to be transferred into an organism as well as the desired gene
6) explain how gene expression may be confirmed by the use of marker genes coding for fluorescent products
7) explain that gene editing is a form of genetic engineering involving the insertion, deletion or replacement of DNA at specific sites in the genome
8) describe and explain the steps involved in the polymerase chain reaction (PCR) to clone and amplify DNA, including the role of Taq polymerase
9) describe and explain how gel electrophoresis is used to separate DNA fragments of different lengths
10) outline how microarrays are used in the analysis of genomes and in detecting mRNA in studies of gene expression
11) outline the benefits of using databases that provide information about nucleotide sequences of genes and genomes, and amino acid sequences of proteins and protein structures
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1. Define the term recombinant DNA
Recombinant DNA refers to DNA molecules that are artificially created by combining genetic material from two or more different sources. This process often involves inserting a gene from one organism into the DNA of another organism, creating a new sequence of DNA that does not naturally exist. The recombinant DNA can then be introduced into a host organism to produce new traits or proteins. This is a fundamental technique in genetic engineering and biotechnology.
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2. Explain that genetic engineering is the deliberate manipulation of genetic material to modify specific characteristics of an organism and that this may involve transferring a gene into an organism so that the gene is expressed
Genetic engineering is the intentional alteration of the genetic material of an organism to change its characteristics in a specific way. This typically involves isolating a desired gene from one organism and introducing it into the genome of another organism. Once inserted, the host organism can transcribe and translate the gene, resulting in the expression of a new protein that gives the organism a new trait. For example, a gene coding for insulin production can be inserted into a bacterium so it produces human insulin for medical use.
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3. Explain that genes to be transferred into an organism may be: extracted from the DNA of a donor organism; synthesised from the mRNA of a donor organism; synthesised chemically from nucleotides
There are three main ways of obtaining a gene for genetic engineering. First, the gene can be extracted directly from the DNA of the donor organism using restriction enzymes that cut the DNA at specific sequences. Second, if the gene is actively expressed in the donor, its mRNA can be isolated and used as a template for synthesising complementary DNA (cDNA) using the enzyme reverse transcriptase. This is useful because mRNA has already had its introns removed. Third, a gene can be constructed from scratch using a known nucleotide sequence. In this method, DNA nucleotides are assembled in the correct order using automated chemical synthesis machines.
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4. Explain the roles of restriction endonucleases, DNA ligase, plasmids, DNA polymerase and reverse transcriptase in the transfer of a gene into an organism
Restriction endonucleases, also known as restriction enzymes, cut DNA at specific nucleotide sequences, often producing "sticky ends" which can easily bond with complementary sequences. DNA ligase is an enzyme that joins together the sugar-phosphate backbones of DNA fragments, effectively sealing the gene of interest into a plasmid vector. Plasmids are small circular DNA molecules found in bacteria that can be used as vectors to carry the gene into the host organism. DNA polymerase is used to synthesise new strands of DNA, especially in processes like PCR. Reverse transcriptase is used to convert mRNA into complementary DNA (cDNA), which is helpful when working with genes that are actively expressed.
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5. Explain why a promoter may have to be transferred into an organism as well as the desired gene
A promoter is a region of DNA located upstream of a gene that initiates transcription by allowing RNA polymerase to bind. Without a promoter, the host cell may not recognise the inserted gene and therefore will not express it. In genetic engineering, a promoter specific to the host organism is often inserted along with the gene to ensure that the gene is transcribed efficiently and at the desired level. For example, in bacteria, a bacterial promoter must be used to ensure proper gene expression.
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6. Explain how gene expression may be confirmed by the use of marker genes coding for fluorescent products
To confirm that a gene has been successfully inserted and is being expressed, marker genes are often included in the vector. These marker genes produce visible traits, such as fluorescence (e.g. the green fluorescent protein gene from jellyfish), allowing scientists to easily identify cells that have taken up the recombinant DNA. If the cells fluoresce under UV light, this indicates that the gene has been successfully integrated and is being transcribed and translated. This is a useful tool for selecting genetically modified cells during the experiment.
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7. Explain that gene editing is a form of genetic engineering involving the insertion, deletion or replacement of DNA at specific sites in the genome
Gene editing is a precise form of genetic engineering where specific changes are made to the DNA sequence of an organism. This can include inserting new DNA sequences, deleting sections of DNA, or replacing existing DNA with altered sequences. Modern techniques such as CRISPR-Cas9 allow scientists to target specific sites in the genome with high accuracy, making gene editing a powerful tool for research, agriculture, and medicine. This differs from older methods, which often inserted genes randomly into the genome.
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8. Describe and explain the steps involved in the polymerase chain reaction (PCR) to clone and amplify DNA, including the role of Taq polymerase
PCR is a technique used to produce millions of copies of a specific DNA sequence in a short amount of time. The process begins by mixing the target DNA, primers (short DNA sequences that start the replication process), nucleotides, and Taq polymerase (a heat-stable DNA polymerase derived from the bacterium Thermus aquaticus). The reaction goes through repeated cycles: denaturation at about 95°C to separate DNA strands, annealing at 50–65°C to allow primers to bind to the target sequence, and extension at 72°C where Taq polymerase adds nucleotides to build new DNA strands. After many cycles, the DNA is amplified exponentially.
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9. Describe and explain how gel electrophoresis is used to separate DNA fragments of different lengths
Gel electrophoresis is a technique used to separate DNA fragments based on their size. DNA samples are placed in wells within an agarose gel and an electric current is applied. DNA is negatively charged due to its phosphate backbone, so it moves toward the positive electrode. Smaller DNA fragments move faster and travel further through the gel, while larger fragments move more slowly. The result is a pattern of bands that can be visualised under UV light after staining with a dye such as ethidium bromide. This technique is commonly used in DNA profiling and forensic analysis.
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10. Outline how microarrays are used in the analysis of genomes and in detecting mRNA in studies of gene expression
Microarrays are tools used to study gene expression and analyse whole genomes. A microarray consists of thousands of DNA probes attached to a solid surface. These probes correspond to known genes. When labelled DNA or cDNA (from reverse-transcribed mRNA) from a sample is applied to the array, it hybridises with complementary probes. The array is then scanned to detect fluorescence, which indicates which genes are present or actively expressed in the sample. This allows researchers to compare gene activity between different cells, tissues, or conditions, such as healthy vs. cancerous tissue.
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11. Outline the benefits of using databases that provide information about nucleotide sequences of genes and genomes, and amino acid sequences of proteins and protein structures
Databases such as GenBank, EMBL, and UniProt store vast amounts of genetic and protein data that are accessible to scientists worldwide. These databases allow researchers to identify genes, compare sequences across species, and predict the function of unknown genes. They also help in identifying mutations, designing primers for PCR, and understanding protein structure and function. Having centralised, curated data reduces duplication of work and accelerates scientific discovery in fields like medicine, biotechnology, and evolutionary biology.
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19.2 Genetic technology applied to medicine
​Students should be able to:
1) explain the advantages of using recombinant human proteins to treat disease, using the examples insulin, factor VIII and adenosine deaminase
2) outline the advantages of genetic screening, using the examples of breast cancer (BRCA1 and BRCA2), Huntington’s disease and cystic fibrosis
3) outline how genetic diseases can be treated with gene therapy, using the examples severe combined immunodeficiency (SCID) and inherited eye diseases
4) discuss the social and ethical considerations of using genetic screening and gene therapy in medicine
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1. Explain the advantages of using recombinant human proteins to treat disease, using the examples insulin, factor VIII and adenosine deaminase
Recombinant human proteins are proteins produced by genetically modified organisms (GMOs) that have had the gene for the human protein inserted into their DNA. These proteins are used in medicine to treat various diseases because they are biologically identical to the proteins naturally produced in the human body. One major advantage is that they are much safer than proteins obtained from animal sources or donated human tissues, which carry a risk of transmitting infections or being rejected by the patient’s immune system. For example, recombinant human insulin, produced by bacteria, is used to treat diabetes and has replaced animal insulin due to its greater purity and fewer allergic reactions. Recombinant factor VIII is used to treat haemophilia A, a condition where patients lack the clotting protein factor VIII. Using recombinant factor VIII avoids the risk of viral contamination associated with plasma-derived factor VIII. Recombinant adenosine deaminase (ADA) is used to treat patients with ADA-deficient severe combined immunodeficiency (SCID), helping restore immune function without requiring a bone marrow transplant.
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2. Outline the advantages of genetic screening, using the examples of breast cancer (BRCA1 and BRCA2), Huntington’s disease and cystic fibrosis
Genetic screening involves testing an individual’s DNA to detect the presence of specific alleles or mutations associated with inherited diseases. This allows early diagnosis, informed decisions about treatment, and the possibility of preventative healthcare. For example, individuals with mutations in the BRCA1 or BRCA2 genes have a significantly higher risk of developing breast and ovarian cancer. Early identification through genetic screening enables them to undertake more frequent screening, lifestyle changes, or even preventative surgery. In Huntington’s disease, a dominant allele leads to neurodegeneration later in life. Genetic screening allows individuals at risk to know whether they carry the defective gene, aiding in life planning and family decisions. Cystic fibrosis is caused by a recessive mutation in the CFTR gene. Screening both partners in a couple can determine if they are carriers, enabling informed choices during family planning and potential use of preimplantation genetic diagnosis (PGD).
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3. Outline how genetic diseases can be treated with gene therapy, using the examples severe combined immunodeficiency (SCID) and inherited eye diseases
Gene therapy is a technique where a normal functional gene is introduced into a person’s cells to correct a genetic disorder. In SCID, a genetic mutation leads to the absence of key immune system components, making affected individuals extremely vulnerable to infections. In some forms, gene therapy involves inserting a correct copy of the ADA gene into the patient’s white blood cells or stem cells using a viral vector. Once inserted, the normal gene allows the cells to produce ADA enzyme, restoring immune function. Inherited eye diseases, such as Leber congenital amaurosis, result from mutations in genes crucial for vision. Gene therapy can deliver the correct gene directly into retinal cells using a harmless virus. This has led to improvements or even restoration of vision in some patients. These successes illustrate the potential of gene therapy to offer long-term or even curative treatment for genetic disorders.
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4. Discuss the social and ethical considerations of using genetic screening and gene therapy in medicine
While genetic screening and gene therapy offer significant medical benefits, they also raise complex ethical and social issues. One concern is privacy and discrimination; individuals identified as having a genetic predisposition to disease might face stigma or difficulties in obtaining insurance or employment. There are also ethical questions around testing embryos or children, who cannot consent, and the potential psychological impact of knowing one’s genetic risks. In gene therapy, especially germline gene therapy (which affects future generations), there is concern about unforeseen consequences and the possibility of using the technology for non-medical enhancements (so-called "designer babies"). Furthermore, access to these technologies may not be equitable, potentially widening health disparities. Overall, while these tools have transformative potential, their use must be governed by careful ethical oversight and public discussion.
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19.3 Genetically modified organisms in agriculture
​Students should be able to:
1) explain that genetic engineering may help to solve the global demand for food by improving the quality and productivity of farmed animals and crop plants, using the examples of GM salmon, herbicide resistance in soybean and insect resistance in cotton
2) discuss the ethical and social implications of using genetically modified organisms (GMOs) in food production
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1. Explain that genetic engineering may help to solve the global demand for food by improving the quality and productivity of farmed animals and crop plants, using the examples of GM salmon, herbicide resistance in soybean and insect resistance in cotton
Genetic engineering is increasingly used in agriculture to address the challenges of feeding a growing global population. It can improve crop yields, reduce losses due to pests and diseases, and enhance the nutritional value or growth rate of organisms. For example, GM salmon have been modified with a growth hormone gene from another fish species and a promoter that ensures year-round expression. As a result, GM salmon grow much faster than non-GM salmon, reducing production time and costs. In herbicide-resistant soybeans, a gene has been inserted that makes the plant immune to glyphosate, a common herbicide. This allows farmers to apply herbicide to control weeds without harming the crop, improving productivity. Similarly, Bt cotton contains a gene from the bacterium Bacillus thuringiensis, which produces a toxin lethal to insect pests such as bollworms. This reduces the need for chemical pesticides and increases cotton yield. These examples show how GMOs can contribute to sustainable agriculture and food security.
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2. Discuss the ethical and social implications of using genetically modified organisms (GMOs) in food production
The use of GMOs in agriculture is controversial and involves a range of ethical, environmental, and socio-economic issues. One concern is environmental safety: GM crops may crossbreed with wild relatives or non-GM crops, leading to genetic contamination. Insect-resistant crops may also harm non-target species such as beneficial insects or contribute to the development of resistant pests. There are also worries about long-term human health impacts, although current evidence suggests GM foods are safe. Ethically, some people object to altering the genetic makeup of living organisms, especially across species barriers. There are also social and economic concerns: GM seeds are often patented and controlled by large corporations, which may place financial pressure on small farmers and reduce seed sovereignty. On the other hand, GMOs offer solutions to food insecurity and may help reduce the environmental impact of farming by lowering pesticide and water use. The key is to balance innovation with regulation and ethical responsibility.