We had already discussed that DNA is made up of polynucleotides. Also, we know that nucleotide contains nitrogenous base pairs. You will be surprised to know that 99.9 per cent of base sequence among humans is the same. It is these differences(0.1%) in the sequence of DNA which make every individual unique in their physical appearance. This might sound like a small amount, it means that there are around three million base pairs that are different between two people.
What is DNA Fingerprinting?
DNA Fingerprinting is a technique used to identify an individual by extracting and identifying the unique base-pair pattern in their DNA.
DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA. In repetitive DNA, a small stretch of DNA is repeated many times. These repetitive DNA are separated from bulk genomic DNA.
The Process of DNA Fingerprinting
- The first step of DNA fingerprinting is to extract DNA (from blood, hair-follicle, skin, saliva or sperm etc.)
- Now the DNA is digested by restriction endonucleases or molecular scissors. This resulted in thousands of pieces of DNA with a variety of different lengths.
- These pieces of DNA were then separated according to size by a process called gel electrophoresis.
- Now the pieces of DNA were transferred (blotted) to the nylon (or nitrocellulose) membrane and then unzipped to produce single strands of DNA.
- Hybridisation using labelled VNTR probe.
- Detection of hybridised DNA fragments by autoradiography. When exposed to radioactivity, a pattern of more than 30 dark bands of DNA appeared on the film. This pattern is called the DNA fingerprint.
Uses of DNA Fingerprinting
- DNA fingerprinting is widely used to find out the real biological parent or offspring in paternity-maternity disputes.
- It is considered to be a sure and best method to identify the real culprit involved in crimes, such as murder, rape etc.
- It has also its application in gene therapy as it helps to provide information regarding some specific alleles.
- DNA fingerprinting is used to identify a dead body that’s too old or damaged to be recognizable.
- It is used to match tissues of organ donors with those of people who need transplants.
- It helps in identifying diseases that are passed down through your family.