Genetic Fingerprinting (AQA A Level Biology): Revision Note
Exam code: 7402
Genetic fingerprinting
Genetic fingerprinting (also known as DNA profiling) is a technique used to identify individuals or assess genetic relationships by analysing non-coding, variable regions of DNA, especially VNTRs (variable number tandem repeats)
The method allows scientists to create a genetic profile, much like a barcode, from DNA samples
Genetic fingerprinting uses a range of gene technologies to complete an individual's unique genetic profile
The process of genetic fingerprinting
DNA extraction
DNA is collected from cells (e.g. blood, saliva, hair root).
The DNA is then purified for analysis.
Amplification by polymerase chain reaction
PCR is used to amplify specific VNTR regions of the DNA to obtain enough material for analysis
This is especially useful when only a small amount of DNA is available
Restriction enzyme digestion
Restriction endonucleases are added to cut the DNA at specific sequences, generating fragments containing VNTRs
DNA fragments are separated based on size using an agarose gel and an electric current
Smaller fragments travel further, creating a distinct pattern of bands
DNA is transferred to a nitrocellulose or nylon membrane and denatured into single strands
DNA probes (radioactive or fluorescent) that bind to VNTR regions are added
Visualisation
The resulting pattern is visualised using X-ray film (for radioactive probes) or UV light (for fluorescent probes)
The banding pattern represents the individual's genetic fingerprint
Determining genetic relationships
Offspring inherit half their VNTRs from each parent
By comparing the banding patterns of DNA profiles:
Parentage can be confirmed (e.g., paternity tests)
Sibling and other family relationships can be inferred
In inheritance disputes or immigration cases, DNA fingerprinting provides evidence of biological relationships
Determining genetic variability in a population
Populations with high genetic variability show many different VNTR patterns
Populations with low genetic diversity will show more similar or repeated banding patterns
This is useful in conservation biology and breeding programs to monitor genetic health
Worked Example
A DNA sample was collected at a crime scene. Investigators obtained DNA from the victim, the crime scene and three suspects. The DNA was extracted, cut with restriction enzymes, amplified using PCR, and then analysed using gel electrophoresis.
The gel electrophoresis results are shown below.
Identify which suspect is most likely to have been at the crime scene. Use evidence from the gel to support your answer.
[1 mark]
Model Answer
Step 1: Read across the results from the gel electrophoresis, looking for a match between the crime scene and the suspects
Suspect 2 matches the DNA found at the crime scene in all visible bands
Examiner Tips and Tricks
In the exam, you will be expected to interpret the results of gel electrophoresis experiments used to separate DNA fragments.
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