Question

For the following question, please answer in essay format( a page and half long minimum)( if hand written please print legibly and be clear about which part of the question are answering, in complete sentences, with as much detail as possible. Thanks!

A single drop of blood is obtained from a crime scene, and the prosecution would like to know if it contains DNA from both the murder victim and a suspect. They supply the forensics laboratory with a sample of blood taken from the body of the murder victim, and a second sample of blood taken from the suspect. If you are the chief scientist in charge of the forensics laboratory, describe the molecular techniques that you would use to determine whether or not DNA from each of the two samples is present in the single drop of blood from the crime scene.

Answer 1

In this ,we have to detect whether the single drop of blood  from the crime scene contains the DNA of the victim and suspect.There are three blood samples.Blood sample of murder victim,suspect and sample taken from the crime scene.For this first we have to isolate the DNA from the samples.Steps for DNA isolation are:

• First lyse the red blood cells and white blood cells present in the blood using detergents.
• Removal of red blood cells and white blood cells.
• removal of membrane lipids.
• treat with protease enzyme so that proteins get denatured.
• Removal of protein and other contaminants.
• RNase treatment
• removal of RNA.
• Add slightly alkaline buffer and elute the DNA.

Following this procedure ,isolate the DNA from the three samples.Then we have to check whether the DNA from the victim and the suspect match with the DNA from the crime scene.For this DNA fingerprinting technique can be used.DNA fingerprinting was developed by Alec Jeffreys.He used satellite DNA as probe that showed high degree of polymorphism.It was called as Variable Number of Tandem Repeats..A probe is a small single stranded DNA that is complementary to the gene of interest.Various steps are:

• isolation of DNA
• digestion of DNA by restriction endonuclease
• separation of DNA fragments by gel electrophorosis.In this DNA gets separated according to size.
• Transferring DNA fragments to synthetic membranes such as nitrocellulose or nylon.This is called southern blotting.
• Then the use of complementary DNA probe to bind to the target DNA that will indicate the presence of target DNA by radioactivity.

Here the DNA probe of murder victim's and suspect should be made and checked with the blood sample from the crime spot.