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Cambridge IGCSE Biology · 0610

Chapter 21: Biotechnology and genetic modification (Part 2)

Definition of genetic modification

Genetic modification (genetic engineering)
The process of changing the genetic material of an organism by removing, changing, or inserting individual genes.
Purpose
This allows cells to perform desired functions, such as producing a specific protein or becoming resistant to environmental factors.

Exam Traps

  • Do not say genetic modification is the same as selective breeding — GM inserts genes directly.
  • Avoid claiming GM always involves whole chromosomes — usually single genes are transferred.

The process of genetic modification

Using the production of human insulin by bacteria as the primary example:

  1. Isolation: The human insulin gene is located and cut out using restriction enzymes, which leave “sticky ends” (short sections of unpaired bases).
  2. Cutting the plasmid: A bacterial plasmid is cut with the same restriction enzymes, creating complementary sticky ends.
  3. Insertion: The human gene is inserted into the plasmid. The enzyme DNA ligase joins the sticky ends together to form a recombinant plasmid.
  4. Transformation: The recombinant plasmid is inserted back into a bacterial cell.
  5. Expression: The bacteria reproduce and express the human gene, synthesising human insulin on a large scale.
Genetic engineering flowchart from human gene isolation through plasmid cutting, recombinant plasmid formation, to modified bacteria in a fermenter
Diagram 1: The genetic engineering process. (1) A human cell and isolation of a gene, (2) a bacterial cell and removal of a plasmid, (3) cutting both with restriction enzymes, (4) formation of a recombinant plasmid using DNA ligase, and (5) modified bacteria reproducing in a fermenter.

Exam Traps

  • Do not say DNA ligase cuts DNA — restriction enzymes cut; ligase joins.
  • Do not confuse transformation (plasmid into bacterium) with translation (protein synthesis at ribosomes).

Examples of genetically modified (GM) crops

Herbicide resistance
Genes are inserted so crops survive being sprayed with weed-killers, increasing yield.
Insect resistance
Crops are modified to be toxic to pests, reducing crop damage.
Nutritional improvement
For example, “Golden Rice” is modified to produce beta-carotene, which the body uses to make Vitamin A, reducing deficiencies in certain regions.

Exam Traps

  • Do not say Golden Rice directly contains Vitamin A — it produces beta-carotene, a precursor.
  • Avoid claiming insect-resistant GM crops need more insecticide — they are modified to resist pests themselves.

Evaluation of GM crops

Advantages
  • Reduces nutritional deficiencies in populations.
  • Improves crop yields and quality, helping to alleviate hunger.
  • Reduces the need for expensive and environmentally harmful insecticides and herbicides.
Disadvantages
  • Potential loss of biodiversity.
  • Risk of creating “superweeds” if herbicide-resistant genes escape to wild plants via crossbreeding.
  • GM seeds are often more expensive for farmers.
  • Long-term health impacts on humans are not yet fully known.

Exam Traps

  • Do not give only advantages or only disadvantages — balanced evaluation is expected.

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