What genetic engineering is
Definition
Genetic engineering
Genetic engineering is changing the genome of an organism by inserting a gene taken from a different organism so that the organism shows a desired characteristic.
Definition
Genetically modified organism
A genetically modified organism is an organism whose genome has had a gene from another organism inserted into it by genetic engineering.
- Genetic engineering is changing the genome of an organism by inserting a gene taken from a different organism so that the organism shows a desired characteristic.
- The genome is the entire genetic material of an organism, so adding a gene to it is a permanent change that is copied every time the cell divides.
- An organism that has been changed in this way is a genetically modified organism, usually shortened to GM.
- Only the gene for the wanted characteristic is moved, so the rest of the organism's genome is unchanged.
- The gene can be taken from a completely different kingdom, so a gene from a bacterium can be placed in a plant, which no amount of breeding could achieve.
Key Idea
Genetic engineering moves one known gene between organisms, so the characteristic that gene controls appears in an organism that could never have inherited it.
Why the transferred gene works
- A gene is a length of DNA that codes for a particular protein, and the order of bases in the gene sets the order of amino acids in that protein.
- The genetic code is universal, which means that the same triplet of bases codes for the same amino acid in every living organism.
- Because of that, the cells of the organism receiving the gene read it in exactly the same way as the cells it came from, and build exactly the same protein.
- The new protein then gives the organism the characteristic, since proteins act as enzymes, as structures and as chemicals that affect other organisms.
- The full chain is therefore gene, then protein, then characteristic, and a question asking why a GM plant is resistant to an insect is asking for that chain.
- The gene must be inserted into cells at an early stage of development, so that as the organism grows every one of its cells carries a copy and the whole organism shows the characteristic.
Example
A bacterial gene that protects a maize plant
- The soil bacterium Bacillus thuringiensis carries a gene that codes for a protein poisonous to caterpillars.
- That gene is inserted into the genome of a maize plant, which then makes the protein in its own leaves and stem.
- A caterpillar that eats the leaf takes in the protein, which damages the lining of its gut, so it stops feeding and dies.
- The maize is unharmed, because the protein only becomes active in the alkaline conditions of an insect gut.
- The plant therefore protects itself, and no insecticide has to be sprayed onto the field.
What genetic engineering is used for
- Insect resistance is added to crops so that the plant makes its own protection and less pesticide is needed.
- Herbicide tolerance is added so that a field can be sprayed to kill the weeds without harming the crop.
- Improved nutrition is added by inserting genes that let a crop make a substance it normally cannot, such as the orange pigment that the human body converts into vitamin A.
- Drought and salt tolerance are added so that crops can be grown on land that is currently too dry or too salty to farm.
- Longer shelf life is added by changing the genes that control ripening, so less of the harvest is lost between the field and the shop.
- Microorganisms are given genes so that they make a human or animal protein, and bacteria carrying the human gene for insulin are the best known example.
- Farm animals have been engineered to produce a useful protein in their milk, from which it can be collected and purified.
Note
Genetic engineering is also used to treat and diagnose human disease, and that use is set out separately in the articles on gene technology in medicine.
How genetic engineering differs from selective breeding
- Selective breeding works only with the alleles a species already has, while genetic engineering can bring in a gene from any organism on Earth.
- Selective breeding takes many generations, while genetic engineering produces the change in a single generation.
- Selective breeding mixes thousands of genes at once, so unwanted characteristics come along with the wanted one, while genetic engineering transfers one identified gene.
- Selective breeding needs no specialist equipment, while genetic engineering needs laboratory facilities, trained staff and approval from a regulator.
Common Mistake
- Do not write that genetic engineering adds a chemical or a hormone to an organism, because what is added is a gene made of DNA.
- Do not say the whole genome is replaced, since only one gene is inserted and the rest of the genome stays as it was.
- Do not use genetic engineering and selective breeding as though they mean the same thing, as one moves a gene directly and the other chooses which parents mate.
Exam technique
Answering questions on genetic engineering
- Define it using the word gene and the word genome, since a definition that only says the organism is changed does not score.
- Explain a characteristic through the protein, so write that the gene codes for a protein and the protein gives the characteristic.
- If a question asks why a gene from a bacterium works inside a plant, the answer wanted is that the genetic code is universal.
- Name the organism the gene came from and the organism it went into, because questions often award a mark for identifying both.
Self review
- Define genetic engineering.
- Explain why a gene taken from a bacterium still produces the same protein when it is placed in a plant cell.
- Describe the chain that links a transferred gene to the characteristic that appears in the modified organism.
- Give three characteristics that have been added to crop plants by genetic engineering.
- Explain why the gene has to be inserted at an early stage of the organism's development.
- Give two differences between genetic engineering and selective breeding.
