What laboratory techniques allow scientists to copy, cut and read DNA?
Describe the techniques of gene technology including restriction enzymes, PCR, gel electrophoresis and DNA profiling
A focused answer to the WACE Year 12 Biology dot point on gene technology techniques. Covers restriction enzymes, recombinant DNA and ligase, the polymerase chain reaction, gel electrophoresis and DNA profiling with their applications.
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What this dot point is asking
SCSA wants you to describe each core technique, explain what it achieves, and understand how they combine in applications such as genetic engineering and forensic DNA profiling. A strong answer states the purpose and the principle of each method.
Restriction enzymes and recombinant DNA
Restriction enzymes are proteins that cut DNA at specific recognition sequences. Many cut in a staggered way, leaving short single-stranded overhangs called sticky ends. Because the same enzyme leaves complementary sticky ends on any DNA it cuts, fragments from different sources can be joined.
DNA ligase then seals the fragments together, producing recombinant DNA: a single DNA molecule combining sequences from more than one source, such as a human gene inserted into a bacterial plasmid.
The polymerase chain reaction (PCR)
PCR makes millions of copies of a target DNA region in a few hours. It repeats a three-step cycle:
- Denaturation: heating to around 95 degrees Celsius separates the two DNA strands.
- Annealing: cooling lets short primers bind to the ends of the target sequence.
- Extension: a heat-stable DNA polymerase builds new complementary strands at around 72 degrees Celsius.
Each cycle doubles the amount of DNA, so the number of copies grows exponentially. PCR is essential when only a tiny sample of DNA is available, such as at a crime scene.
Gel electrophoresis
Gel electrophoresis separates DNA fragments by size. DNA samples are loaded into wells in a gel, and an electric current is applied. Because DNA is negatively charged, it moves toward the positive electrode. Smaller fragments move faster and travel further, so the fragments separate into bands by size. The pattern of bands can then be compared between samples.
DNA profiling
DNA profiling (DNA fingerprinting) compares the banding patterns produced from regions of DNA that vary greatly between individuals. Because these regions differ from person to person, the resulting profile is highly individual (except for identical twins). It is used in forensic identification, paternity testing, and identifying remains.
How the techniques work together
The techniques are usually combined. PCR provides enough DNA to work with; restriction enzymes and ligase build recombinant molecules; gel electrophoresis separates fragments so they can be visualised; and the patterns support profiling or confirm that a gene has been inserted correctly. Understanding the purpose of each lets you follow a whole procedure from sample to result.
Why this matters for continuity
These techniques let humans read, copy and rearrange the genetic material that underlies continuity of species. They make it possible to study genes directly, diagnose genetic conditions, produce useful proteins such as insulin in bacteria, and identify individuals from trace DNA. They are the practical tools behind the applications and ethical debates covered elsewhere in the unit.