Forensic DNA Analysis in Crime Scene Investigation

Forensic DNA Fingerprinting

• Theoretical Background:

  • Introduction to DNA fingerprinting
  • Restriction digest of DNA samples
  • Principle of agarose gel electrophoresis

• Methodology and Protocol:

  • Sample and agarose gel preparation
  • Electrophoresis of DNA samples
  • Analysis and interpretation of results

The Crime

• A medical student from European University Cyprus was found dead at the university parking lot.
• The student was murdered.
• The CSI Nicosia Department asked fellow medical students for assistance in finding the murderer.

The Clues

• Evidence suggests a violent struggle at the crime scene.
• DNA was collected from under the victim's fingernails.

The Suspects

• There are five suspects: the heartbroken ex-girlfriend, the jealous brother, the girlfriend, the campus security guard, and the father of the heartbroken ex-girlfriend.

The Plan

• The students worked together to solve the crime.
• They reviewed the procedures they learned and determined a solution.
• DNA from the suspects was isolated and compared to the DNA from the crime scene using the RFLP technique.
• DNA fingerprinting connects biological evidence to suspects in criminal investigations.

Restriction Fragment Length Polymorphism (RFLP)

• A type of polymorphism caused by variations in DNA sequences recognized by restriction enzymes.
• Short genomic sites (4-8 nucleotides) that differ among individuals are polymorphic.
• DNA is treated with restriction enzymes that cut the DNA into fragments of various lengths.
• Resulting fragments are separated by length, creating a unique pattern for each individual.

Experimental Procedure (Part A: Restriction Digest)

• 10 µl of DNA sample from each suspect and crime scene are transferred to labelled tubes.
• 10 µl of enzyme mix was added to each respective tube.
• The tubes are mixed (flicking gently).
• Tubes are placed in a 37°C water bath for 45 minutes

Experimental Procedure (Part B: Agarose Gel Electrophoresis and Visualization of DNA Fragments)

• A 1% agarose gel is prepared using 100 ml of TAE buffer and 1 g of agarose in an Erlenmeyer flask.
• The agarose is melted in a microwave or on a heat source, and periodically swirled to avoid boiling.
• The gel is poured into a casting tray and allowed to solidify.
• The comb is removed and the gel is placed in an electrophoresis chamber filled with buffer solution.
• 20 µl of dye sample is loaded into each well.
• Electrophoresis is performed for 40 minutes at 100-120V.
• The gel is visualized using a UV transilluminator, and the results are documented and interpreted by the students and instructor.

Experimental Procedure - DNA Samples should contain:

• The following DNA samples and volumes are used
  • Crime Scene (CS) - 10 µl
• Suspect 1 (S1) - 10 µl
• Suspect 2 (S2) - 10 µl
• Suspect 3 (S3) - 10 µl
• Suspect 4 (S4) - 10 µl
• Suspect 5 (S5) - 10 µl
• For each sample - 20 µl of Eco/Pst enzyme mix.

RFLP Markers Inheritance & Test Validity

• Diagram showing inheritance patterns of RFLP markers and potential genotypes (AA, aa, Aa) among family members (parents and siblings)

Agarose Gel Electrophoresis Principle

• Agarose Gel electrophoresis is used to separate nucleic acids by size.
• Nucleic acids migrate through an agarose gel due to an electric field (cathode- to anode+).
• Agarose is a polysaccharide extracted from seaweed.
• DNA is visualized using dyes like GelRed, which bind to DNA and fluoresce under UV light.
• A tracking dye is mixed with the sample to monitor its movement.

Questions:

• Which of the following is FALSE? – Option D
• What is the purpose of Agarose Gel Electrophoresis? – Option (C)

Explore the intricate process of forensic DNA fingerprinting while helping medical students solve a murder case at the European University Cyprus. This quiz covers the theoretical background, methodology, and analysis of DNA samples as students work together to identify the murderer among five suspects. Test your knowledge of forensic science and criminal investigation techniques.