The diagram shows the results of gel electrophoresis used to separate DNA fragments from a crime scene (CS) and three suspects (S1, S2, S3).
[VISUALIZATION: Diagram of a gel electrophoresis result. Label wells at the top for CS, S1, S2, S3. Show distinct bands (DNA fragments) at different positions down the gel for each lane. Ensure the band pattern for S2 matches the CS pattern exactly, while S1 and S3 have different patterns.]
(a) State the property of DNA fragments that allows them to be separated by gel electrophoresis. [1]
(b) Deduce, with a reason, which suspect’s DNA matches the crime scene DNA. [1]
(c) Outline the use of the polymerase chain reaction (PCR) in DNA profiling. [2]
Question
State the property of DNA fragments that allows them to be separated by gel electrophoresis. [1]
Hint
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Consider what makes DNA move in an electric field and how different fragments are sorted.
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Negative charge (due to phosphate groups) OR size/length of fragments.
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Question
Deduce, with a reason, which suspect’s DNA matches the crime scene DNA. [1]
Hint
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Compare the band patterns (number and position of bands) in the CS lane with each suspect’s lane in the visualization.
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Suspect 2 (S2), as the band pattern matches the crime scene (CS).
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Outline the use of the polymerase chain reaction (PCR) in DNA profiling. [2]
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Think about the typical amount of DNA available from a crime scene and what needs to be done before it can be analyzed.
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PCR amplifies small amounts of DNA, creating enough material for analysis like gel electrophoresis, especially from limited crime scene samples.
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