21.3 Genetic modification
- Syllabus
- 0610–2026–2027
- Topic
- 21.3
- Level
- —
Learning objectives
21.3.1Genetic modification as changing• Describe genetic modification as changing the genetic material of an organism by removing, changing or inserting individual genes21.3.3Process of genetic modification using• Outline the process of genetic modification using bacterial production of a human protein as an example, limited to: (a) isolation of the DNA making up a human gene using restriction enzymes, forming sticky ends (b) cutting of bacterial plasmid DNA with the same restriction enzymes, forming complementary sticky ends (c) insertion of human DNA into bacterial plasmid DNA using DNA ligase to form a recombinant plasmid (d) insertion of recombinant plasmids into bacteria (specific details are not required) (e) multiplication of bacteria containing recombinant plasmids (f) expression in bacteria of the human gene to make the human protein21.3.2Genetic modification: (a)• Outline examples of genetic modification: (a) the insertion of human genes into bacteria to produce human proteins (b) the insertion of genes into crop plants to confer resistance to herbicides (c) the insertion of genes into crop plants to confer resistance to insect pests (d) the insertion of genes into crop plants to improve nutritional qualities21.3.4Advantages and disadvantages• Discuss the advantages and disadvantages of genetically modifying crops, including soya, maize and rice
Define genetic modification
Genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes.
Because a gene is a section of DNA that codes for a product, altering an individual gene can give the organism a chosen characteristic or make it produce a chosen protein.
Genetic modification directly changes genes. Selective breeding instead chooses whole organisms as parents and does not directly remove, change or insert an individual gene.
Produce a human protein with genetically modified bacteria
A human gene can be transferred into a bacterial plasmid so bacteria express the gene and manufacture the human protein.
| Step | Required event |
|---|---|
| 1 | Isolate the DNA making up the human gene using a restriction enzyme; this forms sticky ends. |
| 2 | Cut a bacterial plasmid with the same restriction enzyme; this forms complementary sticky ends. |
| 3 | Insert the human gene into the plasmid and use DNA ligase to join the DNA, forming a recombinant plasmid. |
| 4 | Insert the recombinant plasmid into a bacterium; specific insertion details are not required. |
| 5 | Allow bacteria containing the recombinant plasmid to multiply. |
| 6 | The bacteria express the human gene and make the human protein. |
The same restriction enzyme is essential because it produces complementary sticky ends on the human gene and plasmid. Complementary bases can pair before DNA ligase seals the DNA backbone.
Restriction enzymes cut DNA; DNA ligase joins DNA. The inserted material is the human gene, not the finished protein, and the resulting DNA molecule is a recombinant plasmid.
Recognise four uses of genetic modification
Genetic modification transfers or alters genes to give an organism a specified useful outcome.
| Modified organism | Inserted gene gives… | Result |
|---|---|---|
| bacterium | instructions for a human protein | bacteria manufacture a human protein such as insulin |
| crop plant | herbicide resistance | the crop survives herbicide treatment used to control competing weeds |
| crop plant | resistance to insect pests | less pest damage and potentially less insecticide use |
| crop plant | improved nutritional quality | more of a useful nutrient, such as beta-carotene in rice |
The defining action is inserting a gene to create the stated trait. Applying herbicide or insecticide, using yeast in fermentation, and selecting resistant parents are not themselves examples of genetic modification.
Discuss benefits and risks of genetically modified crops
A sound discussion links each genetic change to a benefit and weighs it against economic, environmental, health or ethical risks. The balance may differ between crops such as soya, maize and rice.
| Possible advantage | Possible disadvantage or uncertainty |
|---|---|
| pest-resistant maize can suffer less insect damage, raise yield and require less insecticide, reducing cost and pollution | loss of an insect food source may disrupt food chains, and non-target insects or pollinators may be harmed |
| herbicide-resistant soya lets herbicide remove competing weeds while leaving the crop unharmed | resistance genes may spread by cross-pollination, or selection may favour herbicide-resistant weeds; fewer weeds can reduce biodiversity |
| nutritionally improved rice can provide an additional nutrient such as beta-carotene | the added amount may be insufficient, and unknown consumer health effects or objections may remain |
| resistance to disease, drought, salinity or cold can reduce losses and extend where crops grow | GM seed can cost more, may need repurchasing, and dependence on a narrow range of crops can reduce genetic diversity |
Benefits are not automatic: they depend on the inserted trait, local farming conditions and whether the promised yield, pesticide or nutritional outcome occurs. Risks can be reduced by measures such as preventing cross-pollination, but they still need monitoring.
Herbicide resistance protects the crop from herbicide; it does not make weeds disappear by itself. Separate evidence-based risks from unsupported claims that all GM food is either completely safe or necessarily harmful.