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.

Generated by Claude Opus 4.88 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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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.

Exam-style practice questions

Practice questions written in the style of SCSA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

WACE 20216 marksDescribe the three steps of one cycle of the polymerase chain reaction (PCR), stating the approximate temperature and purpose of each step, and explain why the number of DNA copies grows exponentially.

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A 6 mark answer needs the three steps with temperatures and purposes plus the exponential reasoning.

Denaturation ( $\approx 95^{\circ}C$ ): Heating breaks the hydrogen bonds and separates the double-stranded DNA into two single strands (templates).
Annealing ( $\approx 50$ to $60^{\circ}C$ ): Cooling lets short primers bind to the complementary ends of the target sequence on each template.
Extension ( $\approx 72^{\circ}C$ ): A heat-stable DNA polymerase (e.g. Taq) adds complementary nucleotides from the primers, building a new strand on each template.
Why exponential: Each cycle doubles the amount of target DNA because both strands are copied. After $n$ cycles there are roughly $2^{n}$ copies, so the quantity grows exponentially.

Markers reward each step with its temperature and purpose and the doubling-per-cycle reasoning.

WACE 20235 marksA forensic scientist runs DNA from a crime scene and three suspects on a gel. Explain how gel electrophoresis separates the DNA and how the resulting banding patterns are used to identify a suspect.

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A 5 mark answer needs the separation principle plus the identification logic.

Separation. DNA samples are loaded into wells in an agarose gel and an electric current is applied. DNA is negatively charged (due to its phosphate groups), so it moves toward the positive electrode. Smaller fragments move through the gel more easily and travel further, larger fragments lag behind, so fragments separate into bands by size.

Identification. The banding pattern (profile) reflects the sizes of the variable DNA regions, which differ between individuals. The crime-scene profile is compared with each suspect's profile. A suspect whose bands match the crime-scene pattern at every position is implicated, because an identical pattern by chance is extremely unlikely; a mismatch at any band excludes that suspect.

Markers reward the negative charge and size-based movement, smaller fragments travelling further, and matching banding patterns to identify or exclude a suspect.