Genetic Engineering
Use of Biological Resources
Genetic engineering (also called genetic modification, GM) is the process of deliberately changing an organism's DNA by inserting a gene from a different organism, usually to give it a useful new characteristic
In selective breeding (topic 17), the alleles being shuffled around already exist within the species. Genetic engineering goes much further: it lets scientists take a gene from any species and insert it into the DNA of any other species. This is possible because the genetic code is universal: every living thing uses the same four DNA bases (A, T, G, C) and the same code (three-base codons) to specify amino acids. A human gene placed inside a bacterium still codes for the same human protein.
Some terminology
| Term | Meaning |
|---|---|
| Genetically modified organism (GMO) | Any organism whose DNA has been deliberately altered |
| Transgenic organism | A GMO that contains DNA from a different species (a subset of GMOs) |
| Recombinant DNA | DNA that has been built from pieces of more than one source organism |
| Vector | A "carrier" molecule used to insert the new gene into the host cell. Usually a bacterial plasmid or a virus |
| Restriction enzyme | A bacterial enzyme used to cut DNA at specific base sequences |
| DNA ligase | An enzyme used to join two pieces of DNA together |
A useful memory aid: picture restriction enzymes as the scissors that cut DNA, and ligase as the glue that joins it back together.
Exam tip
Transgenic means a gene moved between species
When a question asks what the term transgenic means (1 mark), the mark is for the species boundary: a gene, allele or piece of DNA has been moved from one species into a different species, so the organism carries a gene from another species. The scheme ignores "genetic modification" on its own and ignores "organism" on its own, because neither says that genes were transferred between species. A bacterium carrying the human insulin gene, a Bt crop and a transgenic tomato all fit the same one-line definition.