12.1.2 DNA Test

• DNA technology has become significant in various fields such as medical science, agriculture, animal and fish resources, and the pharmaceutical industry. It has also contributed to the legal field by ensuring justice in criminal investigations.

• DNA fingerprinting, also known as DNA typing or DNA testing, is a scientific method used to identify individuals based on their DNA profile.

Process of DNA Testing:

1. Sample Collection:

• An organic specimen, such as bone, teeth, hair, blood, saliva, or semen, is collected for testing. This specimen can be from a crime scene or from a victim or suspect.

2. DNA Isolation:

• DNA is extracted from the sample through a chemical process.

3. DNA Fragmentation:

• The DNA is then cut into smaller pieces using restricted enzymes, which are special proteins that break down DNA at specific locations.

4. DNA Sorting (Electrophoresis):

• The fragmented DNA pieces are separated based on their length using a technique called electrophoresis, which uses a gel (agarose or polyacrylamide) to sort the pieces.

5. DNA Probe and Autoradiography:

• A radioactive isotope DNA probe is applied to the sorted DNA, and the probe binds to the DNA pieces on a special nitrocellulose paper.

• The paper is then exposed to X-ray film using an autoradiograph method, which reveals visible bands of DNA.

6. Comparison of DNA Profiles:

• The resulting DNA bands (or DNA map) from the crime scene or specimen are compared with the DNA bands of the victim or suspect.

7. Polymerase Chain Reaction (PCR):

• PCR technology is used for DNA testing with even a small sample. This method amplifies DNA to ensure accurate identification.

Illustration:

• The band patterns obtained from DNA samples can be used to identify suspects. For example, if the DNA band pattern from the crime scene matches that of a suspect, it can confirm the suspect’s presence at the crime scene.

Example:

• A crime scene DNA sample is compared with samples from two suspects. The band pattern from the crime scene exactly matches that of Suspect 1, suggesting they were present at the scene.

This method of DNA fingerprinting is widely used in forensic science to identify perpetrators and confirm their involvement in crimes.