Structure:

• Direct question
• Write what is DNA fingerprinting and the procedure in brief- 50 words
• Its Application

Content:

DNA fingerprinting (also called DNA profiling or DNA typing) is a technique to identify and compare sets of DNA. It is now used for a lots of purposes but forensic is the major field in which it is used.

It was invented by a British geneticist, Sir Alec Jeffreys in 1977 at Leicester university. For the first time it was used in 1983 and then in 1986, to identify the rapist and murderer of two girls in Narboroug, Leisestershire.

Now modern instruments are used for this process, which can identify hundreds of samples in a single day

Principle of DNA fingerprinting

Human genome contains 3 billion base pairs which are arranged in a particular sequence that gives us a unique identity. But still the DNA is every human is almost similar. 90% of the DNA is same in every human beings (about 99.9% nucleotide bases are exactly same in human beings).

DNA fingerprinting is based upon the rest 10% difference in the human DNA. This method is done by matching the uncommon sequence of humans with the suspect's unique sequence.

DNA can be obtained from:

1. Blood,
2. Semen traces/vaginal swab from cloths, saliva,
3. Jair, and skin/tissue

Procedure involved in DNA fingerprinting

1. First of all, the DNA is obtained from any of the sources by using specif techniques such as a high-speed refrigerated centrifuge
2. If the DNA is in poor condition or available only in very small quantity, then many copies of those unique repeating sequence are produced by using the technique of PCR (polymerase chain reaction).
3. Then DNA molecules are cleaved into many fragment, at specific sites using the site- recognizing restriction endonuclease enzyme.
4. These fragments are then sorted out according to their length on an agarose gel slab by the technique called electrophoresis. The fragments get arranged along the gel according to their length and electric charges.
5. Then the DNA, which is double stranded, is then split into single strands by using alkaline chemicals
6. The isolated DNA fragments in the gel are copied onto a nylon nitrocellulose sheet placed on the This technique is called Southern blotting.
7. Special DNA probes (also called hybridization probes) are These contain repeated sequences of nucleotide complementary to those on the repeating sequence. These probes are made radioactive. The radioactive DNA probes bind to the repeat sequences on the nylon sheet. This is called hybridization.
8. An X-ray film is exposed to the nylon sheet to mark the places where the radioactive DNA probes have bound to the DNA fragment. These places are marked as dark bands when X-ray film is This process is called autoradiography.
9. The dark bands on the X-ray film represent the DNA fingerprints, or DNA profiles using which the suspect is identified.

Applications

1. This procedure is mostly used in forensic to identify the criminals
2. It is also used for the paternity test
3. It is used in the study of breeding patterns of animals facing the danger of  extinction
4. It is also used in determining lineages of humans and other animals to ascertain the process of evolution by checking the "genetic markers" which are passed from the ancestors
5. It is used to diagnose the genetic disorders and hereditary disorders like haemophilia, sickle cell anaemia, cystic fibrosis etc
6. It is also used to determine about the antibiotics to which bacteria's are resistant

Advantages of DNA fingerprinting

The biggest advantage of this process is that criminals can be easily be identified through this process. Earlier normal fingerprints were used for this process. Fingerprints can be changed through surgery. But there's no way to change one's DNA sequence. Therefore, it's a promising method.