Genetic engineering — AQA GCSE Biology

Genetic engineering has been applied to crop plants to give useful agricultural characteristics. One aim is resistance to diseases caused by fungi, bacteria or viruses, so fewer plants are lost and yields are more reliable. Another aim is to produce bigger or better fruits, for example by altering genes that control fruit size, ripening or nutritional content. The desired gene is introduced into plant cells, often using a vector such as a plasmid or a virus, and the modified cells are grown into whole plants. Because the new gene is in the plant's genome, it is passed on when the plant reproduces. Farmers may then grow these crops, although their use raises benefits and risks that are considered separately.

Bacteria are useful hosts for genetic engineering because they reproduce rapidly and can be grown on a large scale. To make human insulin, the human insulin gene is cut from human DNA using enzymes and inserted into a bacterial plasmid, which acts as a vector. The plasmid is put into a bacterium, and the modified bacterium is cultured. Because the human gene is now part of the bacterium's genetic material, the bacterium transcribes and translates it to make human insulin. The insulin is then extracted and purified for treating diabetes, where patients cannot produce enough of their own insulin. This process gives a reliable supply of human insulin rather than relying only on animal sources.

Genetic engineering can bring benefits and risks, and people hold different views about it. In agriculture, benefits include crops resistant to disease, improved yields and better fruit quality, which can help food supply. Risks include genes spreading to wild plants, reduced biodiversity, and effects on non-target organisms. In medicine, benefits include reliable production of human insulin and other treatments, while risks include possible side effects, high cost, and ethical concerns about altering genomes. Some people object on religious or ethical grounds, or because they worry about long-term effects and unequal access. A balanced answer explains both sides and recognises that evidence and values both influence decisions.

Genetic engineering is the deliberate transfer of a gene from one organism to another. A gene is a length of DNA on a chromosome that codes for a protein. Enzymes cut the gene out of the donor chromosome, leaving short single-stranded ends called sticky ends. The same enzyme cuts open a vector, often a bacterial plasmid, producing matching sticky ends. The gene is inserted so that complementary bases pair, and ligase joins the DNA. The recombinant plasmid is put into a host cell, such as a bacterium, which then reads the new gene and makes the protein. For example, the human insulin gene can be cut out and transferred into bacteria, which then produce insulin.

A genetically modified crop is a plant whose genetic material has been changed by genetic engineering rather than by selective breeding. The change is made by cutting a useful gene from a donor organism and inserting it into a plant cell, often using a plasmid or a gene gun. The plant cell is then grown into a whole plant, so every cell contains the new gene. Because the gene is present in the plant's cells, the plant can make the protein coded for by that gene. For example, a gene for a natural insect-killing protein can be transferred into maize, making the maize plant able to kill insect pests that feed on it.

Genetic modification can give a crop a gene that protects it against pests or weeds. Insect-resistant GM crops carry a gene from a bacterium that makes a protein toxic to certain insect larvae. When the insect eats the plant, it takes in the protein and dies, so less of the crop is damaged. Herbicide-resistant GM crops carry a gene that lets the plant survive a weedkiller that would normally kill it. A farmer can then spray the field to kill weeds without harming the crop. For example, GM maize can carry a bacterial gene that kills corn borer larvae, and GM soybeans can be sprayed with a herbicide that kills surrounding weeds.

Yield is the amount of usable crop harvested from a given area, often measured in tonnes per hectare. GM crops often give a higher yield because the inserted gene reduces losses. An insect-resistant crop loses less tissue to feeding larvae, so more of the plant's energy goes into growth and grain. A herbicide-resistant crop can be sprayed to remove weeds, so the crop faces less competition for light, water and mineral ions. With less damage and less competition, more biomass is produced and more food can be harvested. For example, a field of GM maize protected from corn borers can produce more grain than the same field of unmodified maize.

GM crops are plants whose DNA has been altered by genetic engineering, often to resist herbicides or pests. A concern is that herbicide-resistant crops allow farmers to spray weedkillers that kill broad-leaved weeds among the crop. Those weeds are food and habitat for wild flowers and insects such as bees, butterflies and beetles. If weed numbers fall, insect populations that depend on them may decline, reducing biodiversity and disrupting food chains. For example, a field of herbicide-resistant oilseed rape may be sprayed so that only the crop survives, removing wild flowers that once grew between the plants. This can lower the number of pollinators and the predators that feed on them. The effect is indirect: the change to the crop leads to changed farming practice, which changes the habitat.

GM crops contain genes transferred from other organisms, so their DNA and proteins differ from those of conventional crops. Some people argue that the long-term effects of eating these foods on human health are not fully known. Possible concerns include new proteins that might cause allergic reactions, changes in nutritional content, or unexpected effects that only appear after many years. Because GM foods have been eaten widely for a relatively short time, some people say there is not enough evidence about lifelong consumption. Others point out that GM foods are tested and regulated before sale, and that no clear harm has been proven. In an exam, present this as a concern held by some people, not as a proven fact. A balanced answer explains the concern and may note the counter-argument that testing and monitoring are carried out.

Inherited disorders are caused by faulty alleles passed from parents to offspring. Modern medical research is investigating whether genetic modification can correct these faults. One approach is gene therapy, in which a normal allele is inserted into a patient’s cells so that the correct protein is made. For example, in cystic fibrosis a faulty allele affects chloride transport, and researchers have tested delivering a working copy of the gene to lung cells. Another approach is to modify cells before birth or in early embryos, though this raises ethical issues. The aim is to overcome the disorder by supplying a functional gene, not to change unrelated characteristics. Success depends on delivering the gene to the right cells and getting it to work there. This is research, so treatments are not yet routine for most disorders.

Genetic engineering changes an organism’s DNA by inserting a gene from another organism. The main steps are: identify and isolate the desired gene using enzymes; cut the gene out with a restriction enzyme, which cuts DNA at a specific sequence; use a vector, often a plasmid or a virus, to carry the gene into the target cell; insert the gene into the vector using DNA ligase, forming recombinant DNA; transfer the vector into the target organism’s cells; and identify the cells that have taken up the gene, often using a marker gene. For example, the human insulin gene can be cut out and inserted into a bacterial plasmid, which is then taken up by bacteria that multiply and produce insulin. The gene must be expressed in the target cell to make the desired protein.

Genetic engineering changes an organism's genotype by transferring a gene from one organism to another. First, enzymes are used to isolate the required gene from the donor DNA. The gene is then inserted into a vector, usually a bacterial plasmid or a virus. The vector carries the gene into the required cells, where it becomes part of the cell's DNA. In animals, plants and microorganisms, the gene is transferred at an early stage of development, so the organism grows and develops with the desired characteristics. For example, a human insulin gene can be inserted into a bacterial plasmid, and the bacteria then produce insulin. Because the gene is present from an early stage, every cell derived from the modified cell can carry it.