How is our knowledge of genetics applied in biotechnology and medicine?
Genetic engineering, the polymerase chain reaction and gene technology, gene therapy, cloning, and the Human Genome Project.
A focused answer to WJEC A-Level Biology Unit 4, covering genetic engineering and recombinant DNA, the polymerase chain reaction and gene probes, gene therapy, cloning, and the Human Genome Project with its ethical issues.
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What this dot point is asking
WJEC wants you to describe genetic engineering and recombinant DNA technology, explain the polymerase chain reaction and gene probes, outline gene therapy and cloning, and discuss the Human Genome Project and its ethical issues.
Genetic engineering
The same restriction enzyme must be used on the gene and the vector because each enzyme cuts a specific sequence, leaving a particular overhang; only matching sticky ends will pair up so ligase can seal them.
PCR and gene probes
Gene therapy, cloning and the genome
Gene therapy treats genetic disorders by inserting a functioning allele, carried by a vector, into a patient's cells; it can be somatic (body cells, not inherited) or, controversially, germ-line (passed to offspring). Cloning produces genetically identical organisms by nuclear transfer (as in Dolly the sheep) or by plant tissue culture, which is widely used to mass-produce identical crop plants. The Human Genome Project sequenced the entire human genome, enabling disease research and personalised medicine but raising ethical issues about genetic privacy, insurance and discrimination.
Examples in context
Example 1. Genetically engineered human insulin. Before the 1980s, diabetics used insulin extracted from pig and cattle pancreases, which could cause reactions. The human insulin gene was inserted into bacteria, which now produce identical human insulin in fermenters. This is the textbook WJEC example of recombinant DNA technology solving a real medical need.
Example 2. DNA profiling in forensics. PCR amplifies tiny DNA samples from a crime scene, and the variable repeat regions are compared between suspect and sample. The exponential power of PCR is what makes profiling possible from a single hair or a drop of blood, a direct application of gene technology to justice.
Try this
Q1. Name the enzyme used to join a gene into a plasmid. [1 mark]
- Cue. DNA ligase.
Q2. Explain why the same restriction enzyme is used to cut both the gene and the plasmid. [2 marks]
- Cue. It produces complementary sticky ends on both, so the gene and plasmid can pair and be joined by ligase.
Q3. Starting from one DNA molecule, calculate how many molecules are present after PCR cycles. [2 marks]
- Cue. molecules.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC 20184 marksDescribe how a gene can be inserted into a bacterium to produce a human protein such as insulin.Show worked answer →
The gene is cut out using a restriction enzyme, which leaves complementary sticky ends.
A plasmid (vector) is cut with the same restriction enzyme so its sticky ends match, and the gene is joined into the plasmid by DNA ligase, forming recombinant DNA.
The recombinant plasmid is taken up by a bacterium (transformation); the transformed bacteria are identified using a marker gene and cultured so they transcribe and translate the gene to make the protein.
Markers reward restriction enzyme and sticky ends, ligase joining into a plasmid vector, transformation, and use of a marker gene.
WJEC 20224 marksThe polymerase chain reaction doubles the number of DNA molecules each cycle. Starting from a single molecule, calculate how many molecules are present after 20 cycles, and outline the three steps repeated in each cycle.Show worked answer →
Each cycle doubles the DNA, so after cycles the number of molecules is from one starting molecule.
After 20 cycles the number is , just over one million molecules.
The three repeated steps are: denaturation (heating to about 95 degrees Celsius to separate the two strands by breaking hydrogen bonds); annealing (cooling to about 55 degrees Celsius so short primers bind to the target sequences); and extension (heating to about 72 degrees Celsius so heat-stable Taq polymerase builds new complementary strands).
Markers reward the value (about one million) and the three correctly described steps.
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Sources & how we know this
- WJEC A-level Biology specification — WJEC (2015)