Genetic engineering — AQA GCSE Combined Science

Genetic engineering has been applied to crop plants to give characteristics useful to farmers and consumers. One aim is disease resistance: a gene from another organism is introduced so the plant can resist a pathogen that would otherwise reduce yield. Another aim is improved fruit, where introduced genes lead to larger fruit or better quality, such as improved flavour, texture or shelf life. For example, a gene giving resistance to a fungal disease could be transferred into a crop so fewer plants are lost. The desired characteristic results because the introduced gene is expressed, making a protein that produces the new trait.

Genetic engineering transfers a desired gene into a bacterial cell so the bacterium makes a human protein. For insulin, the human insulin gene is cut out using enzymes and inserted into a plasmid vector, which is put into a bacterium. The bacterium is grown in a fermenter, where it multiplies and expresses the gene, producing human insulin that is extracted and purified. This works because bacteria reproduce rapidly and can be grown on a large scale. The insulin is identical to human insulin, so it is less likely to cause an immune reaction than animal insulin, and it can be made in unlimited quantities. This links gene transfer, protein synthesis, bacterial growth and medical use.

Genetic engineering can improve crops and medicines, but it raises ethical, environmental and health concerns. In agriculture, benefits include crops that resist pests, diseases or drought, higher yields and reduced pesticide use. Risks include genes spreading to wild plants, effects on non-target organisms and reduced biodiversity. In medicine, benefits include producing human insulin, vaccines and treatments for genetic disorders. Risks include unexpected side effects, high cost limiting access and ethical concerns about altering human genes. Some people object on religious or moral grounds, argue that humans should not alter organisms, or worry that long-term effects are unknown. A balanced answer gives benefits and risks for both areas and explains why objections exist.

Genetic engineering involves modifying an organism's genome by introducing a gene from another organism to give a desired characteristic. For example, the gene that codes for human insulin can be 'cut out' of a human chromosome using enzymes. This gene is then transferred into the DNA of a bacterium. The genetically modified bacterium will then produce human insulin, which can be harvested to treat diabetes. Other examples include transferring genes into plants to make them resistant to diseases, insects, or herbicides. The transfer happens at an early stage of development so the organism develops with the desired characteristics.

Crops produced by genetic engineering are called genetically modified (GM) crops. A gene from another organism is cut out and transferred into the crop plant, so the plant gains a new characteristic. For example, a gene from the bacterium Bacillus thuringiensis gives maize resistance to insect attack, and other genes give crops resistance to herbicides so weeds can be killed without harming the crop. Resistant crops lose less tissue to pests or weeds, so more of the plant's energy goes into growth and grain. This generally increases yield, meaning a larger mass of crop harvested from the same area. Farmers may also use fewer chemical sprays, which can reduce costs and environmental impact.

Genetic engineering can insert a desirable gene, such as one giving herbicide resistance, into a crop plant. This raises two distinct concerns. Ecologically, if farmers spray a herbicide that kills only weeds, wild flowers decline, so insects that feed on them or use them for shelter lose food and habitat, and their populations fall; this can then reduce populations of birds and other animals that eat those insects, so food chains and biodiversity are affected. For human health, some people argue that the long-term effects of eating GM food are not fully known, because testing may not cover many years or all groups of people, and because a new protein might rarely cause an allergic reaction. Others point to evidence that approved GM foods are safe. A balanced answer explains both concerns and the reasoning behind them.

Inherited disorders, such as cystic fibrosis, are caused by faulty alleles inherited from parents. Modern medical research is exploring genetic modification, often called gene therapy, to treat these disorders. The basic idea is to insert a normal, working copy of the allele into the cells of a person with the disorder. This allows the patient's cells to produce the functional protein that was previously missing or faulty. Currently, this research is still at an early stage and treatments are not yet routine. There are also ethical concerns, especially if genetic changes were made to sex cells or embryos, as these modifications would be passed on to future generations.

This content is for Higher Tier students. Genetic engineering involves several main steps to transfer a gene from one organism to another. First, enzymes are used to isolate and 'cut out' the required gene from the donor organism's DNA. This gene is then inserted into a vector. The vector is usually a bacterial plasmid (a small ring of DNA) or a virus. The vector is then used to insert the gene into the required cells of the recipient organism. This transfer is typically done at an early stage in the organism's development, such as an embryo, so that the organism develops with the desired characteristics. For example, inserting the human insulin gene into a bacterial plasmid allows the bacteria to produce insulin.

Genetic engineering begins by identifying the gene coding for a desired protein, such as human insulin. Enzymes are used to cut the DNA, isolating the required gene from the donor genome. The same enzymes cut open a vector, which is typically a bacterial plasmid or a virus. This ensures complementary ends, allowing the gene and vector to join and form a recombinant molecule. The vector then acts as a vehicle to carry the gene into a host cell. Students must understand the role of enzymes in isolation and identify plasmids and viruses as vectors. These detailed enzyme-and-vector steps are assessed at Higher Tier only.

Once the required gene has been inserted into a vector, the vector acts as a delivery vehicle to transfer the gene into the required cells. For example, a recombinant bacterial plasmid can be taken up by bacteria, or a modified virus can inject its genetic material into a plant or animal cell. Inside the host cell, the gene is expressed so the cell manufactures the desired protein, such as human insulin. Students must explain that the vector is not the final destination but the mechanism for inserting the gene into target cells where it can function. This vector-delivery step is assessed at Higher Tier only.

Genetic engineering changes an organism's characteristics by moving a gene from one organism into another. The gene is cut out using enzymes, then inserted into a vector, often a plasmid or virus, which carries it into the recipient cell. Crucially, the transfer happens at an early stage of development, when the organism is an embryo or a single cell, so that every cell produced by subsequent division contains the new gene. For example, a gene for insect resistance can be inserted into a crop plant embryo, so the mature plant and its offspring resist pests. Similarly, a human gene such as the one for insulin can be placed into a bacterium, which then multiplies and produces insulin. The desired characteristic therefore appears as the organism grows and develops.