DNA Analysis

15 03 2010


A homicide has been committed. A middle-aged woman was chocked with a rope. The rope is the only evidence left at the crime scene. What would you do to solve this crime?



In order to find out who the murderer is, you will carry out DNA ANALYSIS. There will be DNA sample left on the rope, which was touched by the murderer.


DNA is the thing that makes you, you. Each person has a unique DNA with unique sequences. This helps C.S.I. figure out who is who by just analyzing evidences, such as blood, saliva, skin cells and figerprints, left at the crime scene.

Do you know the case of the thievery of Mona Lisa from the Louvre in 1911? If you do, do you know how the thief got caught? It was FINGERPRINT. The fingerprint left at the crime scene. It took a long time – two years – for the detectives to figure out who the thief was. It was a man names Vincenzo Peruggia, an employee at Louvre. He left some fingerprints on the protective glass that was shielding the Mona Lisa, and this led to his capture.

What would have happened if each person didn’t have a unique sequence of DNA? Do you now get why DNA is important?

All biological samples contain DNA, or deoxiribonucleic acid. It contains the genetic information that makes each individual unique. DNA differs between each individual; this is why blood, saliva, skin cells and fingerprints have DNA that can be analyzed in an investigation. DNA can be used as a link between a suspect and a crime. Only identical twins have identical DNAs. All cells in human body have DNA, but all DNA in one individual is same regardless of the part of the body we get the DNA from.

In the DNA lab, there are four steps taken to process DNA

  1. Extract
  2. Amplify
  3. Separate
  4. Analyze

1. Extract

The DNA analysts first get the DNA out of the cell to work with it. Bucal swabs are used most often to extract a person’s DNA, since it is painless and easy. Once they get the DNA, they take the DNA out of the cell. DNA is located inside the nuclear membrane. In order to get the DNA out, they lyse the cells and nuclei by dipping the swab into the lysis solution.

2. Amplify

Then, PCR, or polymerase chain reaction, is used to copy the DNA markers millions of times. DNA markers make up less than 0.01% of a person’s DNA, but using PCR makes them stand out despite the big proportion of the rest of the DNA. DNA sample is added to the replicating solution in order to amplify.

3. Separate

After amplification, DNAs have to be sorted by size. This allows us to determine different lengths of markers that are present. The sample from the PCR machine is moved to the Gentic Analyzer, which pushed the DNA through a very small tube filled with a gel-like substance. Small fragments move through faster than large fragments. This is like gel electrophoresis. A laser scans each group of DNA markers in the tube. Then, it records the time the markers exit and send the information to the computer.The computer shows the data from the Genetic Analyzer. A peak is formed each time a group of DNA fragments exit. The computer separates the DNA by size.

4. Analyze

Forensic DNA analysts use DNA profiles to compare DNA samples, because every person’s DNA contains a lot of information. A complete DNA profile will only match one person in one hundred quadrillion. The DNA profile gets processed through the CODIS database that finds the possible matches.



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