#20 The Golden Genes: Forensic DNA Analysis

Hello, and welcome back, folks, to another episode of STEM on the Streets! If you are new here, my name is Aiza, and this is my partner CAI (crime Ai), together, we stroll through the criminal-ridden streets of STEM!

If you haven't read the previous episode, click on the link to read it!

Introduction

If you were here in the previous episode, you would know that we touched the surface of forensic DNA analysis. In today’s episode, we’ll be digging further, learning about how DNA is sampled and DNA analysis and profiling.

DNA Sampling, Profiling (and Analysing)

DNA analysis is a broader term for DNA profiling, which means that DNA profiling is a type of DNA analysis. To simplify further, DNA profiling is a subset of DNA analysis.

DNA can be sampled from different biological materials and fluids, such as hair, blood, tissues, bones, saliva, semen, hair, and other bodily fluids. After it has been sampled, it is removed from the samples and profiled. Then, the samples are compared. The samples must be dealt with with extreme caution to avoid contamination.

To understand the analyzing and profiling process, we must dive into the world of genetics. When an analysis or a cross-analysis is conducted, forensic scientists compare the results of two different DNA samples by using the alleles and loci. So, what are alleles and loci?

(✿◡‿◡) CAI: …

That’s your cue, CAI.

(✿◡‿◡) CAI: Oh, sorry. So a locus (singular of loci) is the location of a specific sort of gene (A gene is the basic heredity unit that encodes for a specific trait, for example, eye colour, blood type, or gender.) within a chromosome (a structure which is made up of strands of DNA). And then, the allele is the different possible versions or sorts of a gene, like having blue eyes or brown; it is the same gene but a variant of it.

Thanks, CAI! Forensic scientists usually collect DNA and analyze and compare the alleles of two different DNA samples to find a match. Here, let’s analyze one together:

The ‘SAMPLE DNA’ is the DNA chart of the sample collected from the crime scene, this could have been collected from different biological materials or fluids. And then ‘SUSPECT DNA’ is the DNA collected from one of the suspects. Give the chart a quick look and try guessing if it is a match. 

Now, if you have given it a close look, you would know that it isn’t a DNA match as the alleles don’t match the sample from the crime scene. You can say one of the major indicators is Amelogenin, which is the sex-determining locus, if you notice for the ‘SAMPLE DNA’ table, the amelogenin is XY, which means the perpetrator was a biological male, and the ‘SUSPECT DNA’ shows that the suspect’s amelogenin is XX which mean the suspect is a biological female. But other than that, the alleles don’t match up. 

The example above is one sort of DNA profiling, here is another one:

These bands upon the film are DNA; each band represents a different number of DNA. This is called DNA fingerprinting. Just like how everyone has their unique fingerprints, everyone has a unique DNA fingerprint. DNA fingerprinting uses the nucleotide sequences of certain regions of human DNA that are special to every individual.

(✿◡‿◡) CAI: Nucleotides are basic units or building blocks of nucleic acids such as DNA (and RNA). Nucleotides consist of a sugar molecule that is attached to a phosphate group and a nitrogen-containing base. There are four bases for DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). 

For DNA fingerprinting, we must begin by taking a DNA sample. Then, we isolate the DNA. After isolating the DNA, we break the DNA into fragments, which are then replicated, and through electrophoresis, we separate the fragments of DNA. Finally, we transfer it onto a film and compare our results.

In the profile, the larger the fragment is, the less far it will travel. As I said previously, everyone has their own unique DNA fingerprint. However, people can share some DNA bands with their parents. So when comparing, the location of the bands is compared:

Below are different DNA samples collected from two suspects and a sample from the crime scene, which one of these is the perpetrator?

If you look closely, Suspect Two and the sample DNA align perfectly, so Suspect 2 is guilty. While some of the bands match with the sample DNA, it is clearly not a match.

Well, that is all for today's short introduction! Until next time!!

This is Aiza Jamil signing out!

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