Advancement of DNA testing in Forensics

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EMBSdiaries

4 min readApr 7, 2021

Anyone who has seen an episode of Mindhunters or Hannibal or CSI will know the fact that catching the killer is only a DNA sample away. Our DNA is a genetic code made up of 4 letters (A, T, G, C) called bases, that are interpreted by our cells to make the molecules and structures that allow our bodies to function. Fun fact, our DNA can stretch from the earth to the sun and back. If unwounded and linked together, the strands of DNA in each of our cells would be 6 feet long. With 100 trillion cells in our body, that means if all our DNA were put end-to-end, it would stretch over 100 billion times, almost 600 round trips to the sun. DNA is responsible for the fact that every person looks different. Although the majority of the DNA between two people are the same but there are some characteristics of the DNA that the scientists use to differentiate the two individuals. DNA testing involves identifying the patterns of genetic material that are unique to almost every individual. The techniques that are used for DNA testing are DNA profiling, DNA typing and DNA fingerprinting. DNA fingerprinting was discovered by Alec Jeffrey while studying how inherited illness passes through families.

DNA TESTING PROCESS

The DNA testing process comprises of four main steps:

Extraction:

This is the first step of testing wherein the nucleus is broken releasing DNA molecules into the solution hence separating DNA from all other cellular material. Two common methods used are Phenol-Chloroform (also called Organic Extraction) and robotic system Maxwell 16.

Quantitation:

This process is used to determine whether the DNA extracted is human and not of any other source such as bacteria. The quality and quantity of DNA is assessed with the help of Quantifiler DNA Human Quantification Kit and then running through an Instrument called ABI PRISM Sequence Detection System.

Amplification:

Herein the DNA is basically xeroxed to produce millions of copies as samples collected from crime scenes is generally of limited quantity. This molecular xeroxing is done via a technique called Polymerase Chain Reaction (PCR)

Capillary Electrophoresis (CE):

After PCR the mixture is passed through an electric current which separates the molecules by size. This separation is then analysed by instruments that determine the match of DNA with the other samples obtained.

How is DNA testing Done?

In this process, a sample of bodily tissue is used to obtain the specific DNA pattern, called the profile of a person. The current DNA testing technique uses polymorphisms called STR (short tandem repeats). STRs are found at many places but mostly at the genetic loci in a person’s DNA. For DNA testing, samples are collected (DNA is found in most cells of the body and body fluids) from a person and then to break open the cells, chemicals are added and then the DNA is extracted and isolated from other cell components. The STRs are cloned many times using polymerase chain reaction to get sufficient DNA to make the profile. The size of the STR is used to calculate the number of times a nucleotide sequence is repeated in each STR. This information is used to determine if the sample comes from a particular person.

Advantages of DNA testing

Scientists have come a long way since 1986(when DNA testing was first used). Now a single drop of blood can be used to identify the suspect. DNA from a crime scene is being used by scientists to make a profile of unidentified victims and potential suspects. The process used to create a profile of the suspect is called DNA Phenotyping. This technique has helped the police to shorten their suspect list and has stopped them from targeting the wrong people.

We may not be fully able to convict someone of a crime but DNA testing sure plays a vital role in today’s forensic analysis and has advanced exponentially since the first case 30 years ago. Not only this has helped us in reducing investigation time but has also developed a psychological fear in the minds of criminals which in turn has reduced the crime rate. So, the next time you’re watching a TV show like CSI and come across all the complicated forensics part, you’d have a pretty good idea about what’s going on!

References

Advancement of DNA testing in Forensics

Published in EMBSdiaries

Written by DIVA BHATIA