Question

briefly describe how PCR and gel electrophoresis can be used to analyse DNA samples from crime scenes.

Answer 1

ANS- PCR(Polymerase chain reaction)---> It is a molecular biology technique In which DNA molecule got replicates and make millions of copies of that particular DNA.In in-vitro condition rather than an organism.

• PCR techniques have the most important thermostable enzyme known as Taq polymerase which has the ability to work at high temperatures without degrading. Apart from this, it utilizes the primer sequence on which the Taq polymerase works and adds a nucleotide to the DNA strand.
• PCR has a wide variety of applications such as medical diagnostic, gene cloning, and one of the important in forensic science to detect the DNA from the crime scene is one of them.

STEPS OF PCR REACTION

1. Denaturation (95-degree Celsius )---> In this the imitation process of PCR reaction in which the double-stranded DNA strands got separated from one another and become single standard. Because at high-temperature hydrogen bonds present between the nucleotide bases that function to joins the 2 strands of DNA got melt and breakdown
2. Annealing(55-65 degree Celsius)--> In this process of PCR reaction the temperature gets cool down that allows the annealing(attachment) of primers to the complementary sequence on single-stranded template DNA.
3. Extension (72-degree Celcius)----> In this process of PCR reaction, the temperature again rises so that Taq polymerase extends the primers, and synthesizing new strands of DNA.

**The cycle of PCR reaction got repeated about 24- 36 times, that takes almost 2-4 hours .the time is based on the length of the DNA region which has to copy

USE OF GEL ELECTROPHORESIS FOR THE VISUALISATION OF PCR RESULTS.

GEL ELECTROPHORESES--->It is the technique in molecular biology in which charged molecules(DNA segments) run in the agarose gel under the influence of electric current got separated on the basis of charge and size. and the ladder is also added in the gel for the identification of DNA segment size.

• This technique is used to visualize the DNA segments, as the DNA segments observed as a band on the gel because of the presence of DNA binding dye (EtBr dye )in the gel.

DNA ANALYSES FROM THE CRIME SCENE (FORSCIENC SCIENCE)

• Assume that on the murder crime scene, the blood of the criminal is found by the policeman. the handle it to a forensic lab where they examine the DNA in a blood sample
• The lab officials examine the specific genetic marker of 4 suspects. and match with blood sample DNA using PCR and gel electrophoresis technique.
• The DNA band is visualized in agarose gel where 1 of the suspect DNA and criminal DNA have the same band size because that's his own DNA so it runs the same distance in agarose gel This whole process of investigating comparing criminal suspect called DNA profiling.