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DNA profiling is the act of collecting/checking for fingerprints, hair, skin, blood, and other bodily fluids that are at a crime scene. These different types of DNA are collected by forensic scientists, specially trained in their field. The process of matching the DNA to the real person it belongs to is called DNA profiling.

Figure 1. Hair being collected at a crime scene.

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DNA profiling is useful because it gives the police a chance to properly identify the people that were present at the time of a crime. Every person's fingerprint is unique to their body, nobody has the same as someone else. DNA profiling is useful in criminal investigations because it can be used to ultimately determine whether or not a suspect is innocent or guilty.

DNA profiling can also be used for paternity tests. This can be done by comparing DNA samples from the mother, father, and child.

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A Gel itself is a Jello-like material. The gel is a maze of agarose molecules held together by hydrogen bonds, which forms tiny pore-like structures. (Khan Academy)

Gel Electrophoresis is a technique used to separate DNA fragments according to their size (Khan Academy).

Figure 3. A Gel Electrophoresis Machine

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DNA samples are loaded into indentations at one end of a gel and then an electric current is applied to it, pulling them through the gel (Khan Academy).

All DNA fragments are negatively charged, so they move towards the positive electrode. All DNA fragments have the same mass but smaller ones travel faster than the larger ones.

Once fragments have been separated, the bands are examined based on their size. A prominent "line" on the gel is called a "band". A band contains a large number of DNA fragments. (Khan Academy)

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Complications of DNA Profiling Used in Investigations

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Complications of DNA Profiling Used in Investigations

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- Evidence that has been planted there on purpose to throw
investigators off.
- Misinterpretation of test results
- Mislabeling of samples.
- Cross-contamination of samples.

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DNA fingerprinting was first used in 1986 in the UK when police requested a professor at the University of Leicester to verify the confession of a suspect for a double rape and murder. Tests that the professor conducted proved that the suspect was not guilty of committing the crimes. This was the first known use of forensic science, proving it's possible efficiency and usefulness in solving crimes.

Although, there has been much controversy around the use of DNA as evidence in the courts. Once it became more prominent in investigations the courts realized that there was a lot of contamination and false evidence that could result in a false conviction. This was first realized in New York when Jose Castro was accused of murdering Vimla Pence and her 2-year-old daughter. They had found blood from Vimla on Castro's watch but this wasn't what was used to convict him. He eventually admitted to committing the crime. The court figured out that the company that had done the testing had used contaminated probes and not followed the necessary controls for a reliable test. Which was why the blood was not directly used as evidence to convince the jury.

Figure 4. Jose Castro surrounded by press during his investigation.

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Distinguish some issues that might occur with DNA profiling used in investigations. (2)

State some ways to prevent these issues from occurring. (4)

Explain the process of Gel Electrophoresis in your own words. (3)

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1. Panneerchelvam, S., and M.N. Norazmi. “Forensic DNA Profiling and Database.” The Malaysian Journal of Medical Sciences : MJMS, Penerbit Universiti Sains Malaysia, July 2003, www.ncbi.nlm.nih.gov/pmc/articles/PMC3561883/.

2. Kelty, Sally, et al. “The Impact of Forensic Evidence on Criminal Justice: Evidence from Case Processing Studies.” Forensic Science and the Administration of Justice: Critical Issues and Directions, pp. 101–120., doi:10.4135/9781483368740.n7.

3. Thompson, William C. “The Potential for Error in Forensic DNA Testing.” Gene Watch Page, Council for Responsible Genetics, www.councilforresponsiblegenetics.org/genewatch/GeneWatchPage.aspx?pageId=57.

4. “Gel Electrophoresis (Article).” Khan Academy, Khan Academy, www.khanacademy.org/science/biology/biotech-dna-technology/dna-sequencing-pcr-electrophoresis/a/gel-electrophoresis.