Understanding How DNA Fingerprinting Is Done

DNA fingerprinting:-

DNA fingerprinting which is also known as DNA profiling, genetic fingerprinting, DNA typing etc. DNA fingerprinting came into picture in 1984 when Alec Jeffrey noticed that there was a highly variable DNA sequence or highly variable DNA repeats in between the genes. And this variable repeats or this variable DNA is unique for each and every individual that gives an idea that DNA can tell a lot about an individual also you can also look into the DNA and say that one person is related to another.

 So what essentially this mean in humans when we take a linear sequence of DNA?

 We know that we contain multiple genes. All these genes are going to be the same for all the individuals the same as there will be different copies of these genes or different alleles of these genes present in the different individuals. Now in between these genes we have a non-coding region in the DNA, this is what we used to call as junk DNA but now we know that it is very important. Now this non-coding region is the one which shows very high variability.  The region in between genes where we see high variability, is highly variable in each and every individual. Now in this non-coding region we will see repeats of the DNA letters multiple times say for example there is G, A, T,A sequence and this sequence will be repeated over and over again maybe like 10 times twenty times fifty times hundred times this is very unique for each and every individual. That multiple repeats of some short DNA sequences present is called short tandem repeats. 

This short tandem repeats or what we call STR's are very unique for each and every individual so this non-coding region of DNA contains multiple short tandem repeats.

DNA fingerprinting actually utilizes this property. We will see what exactly or how exactly this helps. Say for example we have three different individuals. we have individual 1 2 & 3 as we know they will all have the same gene that means different allele or different copies of the gene but the difference will be in the non-coding region. There is a repetitive short sequence which is present and that differs in every digit so we know for individual 1 this STR sequence is repeated for quite a number of time it maybe big but for individual number 2, the STR is different and same for individual 3 it is very different. So we can say in each and every non-coding region it differs for every individual. This is what the concept is telling that STR are highly variable. DNA short tandem repeats are different for every individual and that is going to give us the fingerprinting.

What is the mechanism of DNA fingerprinting? how it is going to utilize this STR and give you a profiling ?

gel electrophoresis

So what we do for DNA fingerprinting is we will cut these STR's using restriction enzyme that would be the first step. Once we isolate these short tandem repeats or STR, we are going to multiply them or increase them in number using polymerase chain reaction or PCR. Once we have good amount of sample, we are going to separate these using gel electrophoresis. Now we know that we can separate DNA on the agarose gel. Hence we are going to separate them using gel electrophoresis. AS DNA is negatively charged it is going to get pulled towards the positive charge. So based on the size of the STR of that particular segment it is going to get separated. This is how it is going to separate for all three individuals.

 

Understanding How DNA Fingerprinting Is Done

Looking at the above separation pattern in the image, this is called as the fingerprinting of that particular individual.

 Now how is this going to help us? what are the applications of this?

Understanding How DNA Fingerprinting Is Done in Forensics

DNA fingerprinting can help us in forensic to solve a crime or for paternity test. So let's take one example and see the application of DNA fingerprinting. Let's take a murder case and see how we can utilize DNA fingerprinting to solve a murder scene. Say for example we have got a blood sample at a murder site which is not of the victim but it is of some others blood sample and we have three suspect. what we're going to do is we're going to take sample from all three suspects and the sample that we have got at the murder site, we run it on agarose gel and what we get is a fingerprint something like all the segments based on their size have got separated on the gel. Hence by matching the STR sequence with that of the suspects we can determine the killer. The principle being that the STR of the sample matches with the STR sequence of the suspect. And so this is how DNA fingerprinting helps.

Solving paternity cases

This is also helpful for solving paternity case to find out the biological father of a child. You can take the sample of the child and the father and you can run the similar tests. If you see the similarities in the STR region, you can conclude that he is the rightful father of that child. So that's how DNA fingerprinting works.