OCR GCSE Biology B (J257) — Genetics and the Genome
How do we convince a bacterium to manufacture a human hormone? We use genetic engineering, which allows scientists to transfer genes between entirely different species much faster than traditional selective breeding.
First, the desired gene is isolated and "cut out" of the donor DNA using restriction enzymes. A vector (such as a bacterial plasmid or a virus) is then cut open using the exact same restriction enzyme.
Because the same enzyme is used, it leaves complementary unpaired bases called "sticky ends" on both the gene and the vector. An enzyme called DNA ligase is used to glue these sticky ends together, forming recombinant DNA.
This recombinant vector is inserted into a host cell (like E. coli bacteria) to create a transgenic organism. Scientists use marker genes, such as antibiotic resistance, to identify which cells successfully took up the plasmid. These cells are then grown in a fermenter under controlled conditions to mass-produce the desired protein, such as human insulin.
We can now grow rice that helps prevent blindness by producing its own vitamins. "Golden Rice" is genetically modified with genes from daffodils and bacteria to produce beta-carotene, which the human body converts into Vitamin A.
Gene technology also boosts crop yields through pest resistance. Bt crops (like maize) contain a gene from the bacterium Bacillus thuringiensis. This gene produces a toxin that is lethal to caterpillars but harmless to humans and non-target animals, drastically reducing the need for chemical insecticides.
Similarly, crops can be engineered for herbicide resistance (e.g., "Roundup Ready" soya). Farmers can spray entire fields with herbicides to kill competing weeds without harming the crop. Genes for "antifreeze" proteins or salinity tolerance can also be added to help crops survive extreme climates.
Solving one farming problem can accidentally create a severe ecological crisis. Relying heavily on GM monocultures and herbicides reduces biodiversity, killing wildflowers and removing crucial food sources for pollinators like bees.
Furthermore, herbicide-resistant crops can accidentally create a superweed. This happens through gene flow, which occurs via cross-pollination when GM pollen fertilises wild plant relatives (e.g., GM oilseed rape breeding with wild charlock).
When farmers apply herbicides, it acts as a selection pressure. Only the wild hybrids that inherited the resistance gene survive via natural selection. These superweeds proliferate, creating a population that cannot be controlled by standard chemicals, forcing the use of increasingly toxic alternatives.
Animal insulin used to cause dangerous immune reactions, but modern GM insulin is a perfect match for your body. GM insulin is chemically identical to human insulin because it is produced using the human gene, significantly reducing allergy risks.
It is also much safer because it carries no risk of animal-to-human disease transfer. Furthermore, it meets the ethical and religious dietary requirements for Vegan, Halal, and Kosher patients.
However, gene technology can introduce new proteins into foods (like Brazil nut genes in soya) that act as an allergen, triggering immune responses. In medicine, traces of host proteins from the E. coli used in fermenters can cause contamination reactions, and viruses used as vectors in gene therapy can trigger severe inflammation.
Thanks to the Human Genome Project, we can now identify faulty alleles and move towards personalized medicine, tailoring drugs to a patient's specific genetic profile. Note that all new GM medicines must undergo rigorous clinical trials before public use.
Imagine a farmer who is legally banned from saving seeds from their own harvest for the next year. Large biotech companies use a patent to create a monopoly on GM seeds (often lasting 20 years).
Technologies like "Terminator Technology" create plants with sterile seeds. This forces farmers, especially in developing nations, into a cycle of debt as they must buy expensive new seeds annually.
Ethically, many object to altering genomes, arguing humans should not be "playing God" with the natural order. There are specific concerns around germline modification (altering embryos), as the changes are heritable and the future generation cannot give informed consent.
Socially, there is fear of genetic discrimination, where employers or insurance companies might deny opportunities based on genetic predispositions. Some also fear a shift from therapeutic medicine to enhancement ("designer babies"), creating a genetic underclass based on wealth.
In conclusion, while gene technology offers immense benefits for global food security and mass-producing life-saving medicines like insulin, it carries profound risks. These include irreversible ecological impacts like superweeds and significant ethical concerns regarding corporate monopolies and the morality of altering human lineages. Careful regulation is essential to balance these outcomes.
Students often confuse selective breeding with genetic engineering. Remember that selective breeding takes many generations and involves the same species, whereas genetic engineering is fast and transfers genes between completely different species.
When explaining the risk of superweeds for a high-mark question, examiners look for the specific mechanism: always mention 'gene flow via cross-pollination with wild relatives'.
For 'Discuss' questions on gene technology, you must present a balanced argument. State a clear benefit (e.g., increased food security) and weigh it against a specific consequence (e.g., ecological disruption or monopolies), before writing a final concluding sentence.
OCR B mark schemes frequently look for the word 'vector' when describing the role of a bacterial plasmid or virus in the genetic engineering process.
When explaining why GM insulin is safer than animal insulin, use the exact phrase 'chemically identical to human insulin' rather than just saying 'it is human'.
Genetic engineering
The process of changing the genome of an organism by introducing a gene from another organism to give it a desired characteristic.
Restriction enzymes
Enzymes used to cut DNA at specific base sequences, often leaving complementary sticky ends.
Vector
A DNA molecule, such as a bacterial plasmid or a virus, used as a vehicle to artificially carry foreign genetic material into another cell.
Bacterial plasmid
A small, circular piece of DNA found in bacteria that can act as a vector in genetic engineering.
DNA ligase
An enzyme used to join DNA fragments together, specifically gluing the sticky ends of the gene and vector.
Recombinant DNA
DNA that has been formed artificially by combining genetic material from different organisms.
Transgenic organism
An organism that contains DNA from a different species introduced via genetic engineering.
Marker genes
Genes, such as those for antibiotic resistance, used to identify which cells have successfully taken up the recombinant vector.
Pest resistance
A trait introduced into crops (like Bt crops) allowing them to produce toxins that kill specific insect pests.
Bt crops
Crops engineered with a gene from Bacillus thuringiensis that produces a toxin lethal to insect larvae.
Herbicide resistance
A genetically engineered trait allowing crops to survive the application of specific weed-killing chemicals.
Biodiversity
The variety of plant and animal life in the world or in a particular habitat, which can be threatened by GM monocultures.
Superweed
A wild plant that has acquired a gene for herbicide resistance via gene flow, making it difficult to control.
Gene flow
The transfer of genetic material from one population to another, such as via pollen transfer.
Cross-pollination
The transfer of pollen from the flower of one plant to the flower of a plant having a different genetic constitution.
Selection pressure
An environmental factor, like herbicide application, that confers a survival advantage on individuals with specific traits.
Allergen
A substance, usually a new or foreign protein, that causes an abnormal immune response.
Personalized medicine
Medical treatment tailored to the individual characteristics of each patient based on their genetic profile.
Patent
A legal protection giving an inventor or biotech company exclusive rights to an invention, such as a GM seed, for a limited time.
Monopoly
A situation where a single company owns nearly all the market for a product, preventing competition.
Germline modification
Altering DNA in human embryos, sperm, or eggs so the genetic change is heritable by future generations.
Put your knowledge into practice — try past paper questions for Biology B
Genetic engineering
The process of changing the genome of an organism by introducing a gene from another organism to give it a desired characteristic.
Restriction enzymes
Enzymes used to cut DNA at specific base sequences, often leaving complementary sticky ends.
Vector
A DNA molecule, such as a bacterial plasmid or a virus, used as a vehicle to artificially carry foreign genetic material into another cell.
Bacterial plasmid
A small, circular piece of DNA found in bacteria that can act as a vector in genetic engineering.
DNA ligase
An enzyme used to join DNA fragments together, specifically gluing the sticky ends of the gene and vector.
Recombinant DNA
DNA that has been formed artificially by combining genetic material from different organisms.
Transgenic organism
An organism that contains DNA from a different species introduced via genetic engineering.
Marker genes
Genes, such as those for antibiotic resistance, used to identify which cells have successfully taken up the recombinant vector.
Pest resistance
A trait introduced into crops (like Bt crops) allowing them to produce toxins that kill specific insect pests.
Bt crops
Crops engineered with a gene from Bacillus thuringiensis that produces a toxin lethal to insect larvae.
Herbicide resistance
A genetically engineered trait allowing crops to survive the application of specific weed-killing chemicals.
Biodiversity
The variety of plant and animal life in the world or in a particular habitat, which can be threatened by GM monocultures.
Superweed
A wild plant that has acquired a gene for herbicide resistance via gene flow, making it difficult to control.
Gene flow
The transfer of genetic material from one population to another, such as via pollen transfer.
Cross-pollination
The transfer of pollen from the flower of one plant to the flower of a plant having a different genetic constitution.
Selection pressure
An environmental factor, like herbicide application, that confers a survival advantage on individuals with specific traits.
Allergen
A substance, usually a new or foreign protein, that causes an abnormal immune response.
Personalized medicine
Medical treatment tailored to the individual characteristics of each patient based on their genetic profile.
Patent
A legal protection giving an inventor or biotech company exclusive rights to an invention, such as a GM seed, for a limited time.
Monopoly
A situation where a single company owns nearly all the market for a product, preventing competition.
Germline modification
Altering DNA in human embryos, sperm, or eggs so the genetic change is heritable by future generations.
