Genetic modification — definition and four examples
Genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes. A gene is a section of DNA coding for one protein. The four named examples: human genes into bacteria to make human proteins such as insulin; genes into crops for herbicide resistance; genes into crops for insect-pest resistance; genes into crops for better nutrition, as in golden rice, engineered to make beta-carotene.
(Extended) Recombinant DNA — the six steps
Recombinant plasmid production, in the syllabus order. (1) A restriction enzyme cuts human DNA at a specific base sequence, isolating the gene and leaving sticky ends. (2) The SAME enzyme cuts open a bacterial plasmid, leaving complementary sticky ends. (3) DNA ligase joins the gene into the plasmid, forming a recombinant plasmid. (4) It is inserted into a bacterium. (5) The bacteria multiply. (6) They express the gene and make the protein.
(Extended) GM crops — both sides of the argument
The syllabus names soya, maize and rice. Advantages: higher yield, as less is lost to insect pests or weed competition; less insecticide or herbicide spraying; better nutrition, such as beta-carotene in golden rice. Disadvantages: single-variety plantings are genetically uniform, so a pest that overcomes the inserted gene can sweep the crop; pollen carries the gene to non-GM crops and wild relatives; long-term effects are untested; few companies control seed supply.
Drawn from real examiner reports.
Plasmid, not bacterial chromosome
The human insulin gene goes into a plasmid — a small circular loop of DNA separate from the bacterial chromosome — forming a recombinant plasmid, which then enters the bacterium. Naming the bacterial chromosome, or writing only that the gene was "put into the bacteria", misses the specific term the mark scheme credits.
Flagged s23 P23 Q39 — many wrote "bacterial chromosomes" or described the process without naming the plasmid
Genetic modification ≠ selective breeding
Selective breeding chooses existing organisms of the same species that show a wanted feature and crosses them over many generations; no gene is inserted, removed or changed. Genetic modification alters the genes directly and can move a gene between completely different species. Describing crosses when the question asked for GM scores nothing.
Flagged s22 P42 Q6d · w22 P43 Q3vi — candidates named selective breeding when asked for genetic modification
"Biotechnology" alone earns nothing
Examiners judged the single word "biotechnology" too vague to credit when the question asked for genetic modification or genetic engineering. Name the process precisely, and on Extended papers name a mechanism alongside it — restriction enzyme, plasmid, DNA ligase — rather than a broad field of study.
Flagged s22 P42 Q6d · w22 P43 Q3vi — "biotechnology" was judged too vague and not credited alone
Ligase joins, restriction enzyme cuts
A restriction enzyme cuts DNA at a specific base sequence, isolating the gene and opening the plasmid. DNA ligase does the opposite job — it seals the gene into the cut plasmid. Swapping the two, or offering DNA polymerase (which copies DNA) as the joining enzyme, loses the named-term mark at that step.
Same enzyme, not just any enzyme
Sticky ends only pair up because the SAME restriction enzyme cut both the human DNA and the plasmid, recognising the same base sequence and leaving complementary overhangs. Writing that a restriction enzyme cuts each one, without stating that it is the same enzyme, drops the explanation mark.
Pollution answers miss the real risk
Asked for a disadvantage of large-scale GM planting, candidates reach for pollution or global warming. The credited mechanism is genetic: a huge area of one variety is genetically uniform, so a new pest or pathogen that overcomes the inserted resistance gene meets few or no survivors and can sweep the whole crop.
Flagged w22 P42/43 Q4a iii · s23 P33 Q8d ii — generic pollution answers given; genetic consequences of reduced variation rarely mentioned
"Changing DNA" is half a definition
The definition needs the full phrase: changing the genetic material of an organism by removing, changing or inserting individual genes. Answers such as "adding new DNA" or "mixing DNA together" give only part of the idea and omit the three named mechanisms the mark scheme lists.
Outline means six steps, in order
Restriction enzyme and sticky ends; the same enzyme cuts the plasmid; DNA ligase forms the recombinant plasmid; insertion into the bacterium; multiplication; expression. A skipped step, a reversed order or an unnamed enzyme costs the mark even when the general idea is right.
Discuss demands both sides
Give one advantage with its mechanism and one disadvantage with its mechanism — distinct points, not the same idea reworded on each side. A one-sided list, however long, caps the marks available on a discuss question.
Name the crop, then the mechanism
Anchor the answer in a specific case — insect-resistant maize, golden rice, herbicide-resistant soya — then say what the inserted gene actually does. Generic statements that GM crops are good or bad, with no named crop or mechanism, score little.
Percentage change: divide by the original
For yield or nutrient comparisons, subtract the two figures then divide by the ORIGINAL (non-GM) value, not the new one. Dividing by the GM figure is the standard slip and loses the accuracy mark even when the working is otherwise correct.
Genetic modification (genetic engineering) is defined as changing the genetic material of an organism by removing, changing, or inserting individual genes.
A gene is a section of DNA (deoxyribonucleic acid) that codes for one particular protein.
The four named syllabus examples of genetic modification:
| Example | Gene inserted into | Purpose |
|---|---|---|
| Human insulin production | Bacteria | Bacteria produce human insulin protein for treating diabetes |
| Herbicide resistance | Crop plants | Crop survives herbicide spraying that kills competing weeds |
| Insect-pest resistance | Crop plants | Crop is harmed less by insect pests, reducing need for insecticide |
| Improved nutritional quality | Crop plants | Crop produces a nutrient it would not otherwise make (e.g. "golden rice" — beta-carotene) |
Define genetic modification (genetic engineering).
(a) Describe what is meant by genetic modification. [2]
(b) State TWO named examples of genetic modification given in the syllabus, other than human insulin production. [2]
