Topic H: Biotechnology (Elective)

This elective examines the techniques that allow scientists to read, copy and alter genetic material, and how they are applied in medicine, agriculture and industry. You study genetic engineering and the tools that make it possible, methods of cloning and amplifying DNA, the production and uses of genetically modified organisms, and the social and ethical questions involved. DSE rewards candidates who not only describe the techniques accurately but also discuss their benefits and risks in a balanced, evidence-based way.

Tools of genetic engineering

Genetic engineering is the deliberate transfer of a gene from one organism into another. It depends on a set of molecular tools. Restriction enzymes cut DNA at specific base sequences, producing fragments with matching ends, and DNA ligase joins fragments together. A vector, often a bacterial plasmid or a virus, carries the chosen gene into the host cell. Because the genetic code is universal, a gene from one species will still be read and produce the same protein in another. You should be able to describe the role of each tool, explain why restriction enzymes and ligase work as molecular scissors and glue, and understand that the universality of the code is what makes transferring genes between species possible.

Producing a genetically modified organism

To make a genetically modified organism, the desired gene is first identified and cut out using a restriction enzyme. The gene is then inserted into a vector, typically a plasmid cut with the same enzyme so the ends match, and sealed in place with DNA ligase to form recombinant DNA. The vector is introduced into host cells, often bacteria, which take up the plasmid and, as they multiply, copy and express the gene. Cells that have successfully taken up the gene are selected and grown in large numbers to produce the protein. The classic example is producing human insulin from genetically modified bacteria. You should be able to put these steps in the correct order and explain why the same restriction enzyme is used on both gene and plasmid.

The polymerase chain reaction

The polymerase chain reaction, or PCR, is a technique for making many copies of a specific piece of DNA from a very small starting sample. The DNA is repeatedly heated to separate its two strands, cooled so that short primers attach to mark the region to be copied, and warmed so that a heat-stable enzyme builds new complementary strands. Each cycle doubles the amount of target DNA, so after many cycles millions of copies are produced. PCR is invaluable when only a trace of DNA is available, for example in forensic science, diagnosis of disease and research. You should be able to outline the repeated heating and cooling steps, explain why the amount doubles each cycle, and state why amplifying DNA is useful.

Cloning

A clone is a group of genetically identical organisms or cells produced from a single parent without sexual reproduction. Plants are cloned naturally by vegetative reproduction and artificially by tissue culture, in which small pieces of tissue are grown on sterile nutrient medium to produce many identical plants, useful for multiplying desirable or rare varieties. Animals can be cloned by techniques such as transferring the nucleus from a body cell into an egg whose own nucleus has been removed, as in the cloning of Dolly the sheep. Cloning preserves a particular genotype exactly. You should be able to describe tissue culture and outline nuclear transfer, explain the advantages of cloning a chosen organism, and note the drawback of reduced genetic variation in clones.

Applications of genetically modified organisms

Genetically modified organisms have many uses. In medicine, modified bacteria produce human proteins such as insulin and growth hormone, and gene therapy aims to treat genetic disorders by supplying a working gene. In agriculture, crops are engineered for resistance to pests or herbicides, for higher yield, or for improved nutrition, such as rice enriched with a vitamin A precursor. In industry, modified microbes make enzymes and other products. These applications can increase food production, reduce pesticide use and provide cheaper medicines. You should be able to describe at least one medical and one agricultural application, explain the intended benefit in biological terms, and recognise that each application also brings possible risks that must be weighed against its advantages.

Risks and bioethics

Biotechnology raises important ethical, social and environmental questions. Concerns about genetically modified crops include possible effects on health, the escape of modified genes into wild populations, harm to non-target organisms, and the economic control of seeds by large companies. Cloning and gene therapy raise questions about safety, consent and how far it is acceptable to alter living things, especially humans. Supporters point to benefits such as more food, less pesticide and new medical treatments. A good answer presents both sides, uses biological reasoning rather than emotion, and recognises that society must balance benefits against risks through regulation. You should be able to discuss a named application, set out arguments for and against, and reach a reasoned conclusion rather than simply listing points.

DNA technology in identification

DNA technology is widely used to identify individuals and relationships. Because each person's DNA, apart from identical twins, is unique, a DNA profile can be made by cutting DNA into fragments and separating them by gel electrophoresis, which sorts the fragments by size to give a banding pattern. PCR allows a profile to be made from tiny samples. DNA profiling is used in forensic investigations to link a suspect to a crime scene, in paternity testing, and in identifying remains. Care is needed because samples can be contaminated and patterns must be interpreted statistically. You should be able to outline how a DNA profile is produced, explain why electrophoresis separates fragments by size, and describe the main uses and limitations of the technique.