harsh vardhan dna fingerprinting

DNA FINGERPRINTING

HARSH MOONAT CLASS XII “A”

What is DNA Fingerprinting?

A technique used by scientists to distinguish between individuals of the same species using only

samples of their DNA. It is also known as DNA PROFILING

Why DNA Fingerprinting?

The chemical structure of everyone's DNA is the same. The only difference between people (or any animal) is the

order of the base pairs. The information contained in DNA is determined primarily

by the sequence of letters along the zipper. Using these sequences, every person could be identified

solely by the sequence of their base pairs (except identical monozygotic twins)

There are millions of base pairs, the task would be very time-consuming. Instead, scientists are able to use a shorter DNA Fingerprinting method, because of repeating patterns in DNA.

These patterns do not, however, give an individual "fingerprint," they are able to determine whether two DNA samples are from the same person, related people, or non-related people.

Historical background

• DNA fingerprinting was developed in 1984 by Alec. J. Jeffrey at the University of Leicester

• He was studying the gene of myoglobin.

• Dr. V.K. Kashyap and Dr. Lalji Singh started the DNA fingerprinting technology in India

Alec. J. Jeffrey

Principle of DNA Fingerprinting

DNA carries a short repetitive sequences of nucleotides which do not code for proteins and specific for each person.

These sequences are called variable number of tandem repeats (VNTR's) or minisatellite.

In DNA Fingerprinting VNTR are used as probe because of its high degree of polymorphism.(polymorphism is the occurrence of inheritable mutations in a population at high frequency)

Biological materials used for DNA fingerprinting

Blood

Hair

Saliva

Semen

Body tissue cells

Bone

Steps of DNA Fingerprinting

Step ONE : Isolation of DNA

Isolation of DNA from a nucleus and purification by chemical method or

centrifugation.


Step TWO: Amplification

If only a small amount of DNA is available it can be amplified using the

polymerase chain reaction (PCR)


Step Three: digestion

The DNA is cut into fragments using restriction enzymes which cuts DNA at a specific base sequence.

The sections of DNA that are cut out are called restriction fragments.


Step Five: Southern blotting

The distribution of DNA pieces is transferred to a nylon or

nitrocellulose sheet by placing the sheet on the gel and soaking them

overnight. ( Edwin Southern : A Biochemist)

Steps of DNA FingerprintingStep Four: Separation of DNA

Fragments

Fragments are separated on the basis of size using a process called gel electrophoresis.

DNA fragments are injected into wells and an electric current is applied along the gel.

DNA is negatively charged so it is attracted to the positive end of the gel.

The shorter DNA fragments move faster than the longer DNA fragments. DNA is separated on basis of size.


Step Seven: Autoradiography

An X-ray film is developed for this binding pattern and a photographic

copy of the DNA bands is obtained. This pattern is called

DNA Fingerprint.


Step six: Hybridization

Special radioactive DNA probes contains repeated sequences of

bases complementary to those on VNTRs. These radioactive probes

binds to the VNTRs on the nitrocellulose or nylon membrane and produce a fluorescent image.

Practical Applications of DNA Fingerprinting

Paternity and Maternity Tests(person inherits his or her VNTRs from his or her parents. Parent-child VNTR pattern analysis has been used to solve standard father-identification cases )

Personal Identification(The notion of using DNA fingerprints as a sort of genetic bar code to identify individuals)

Can someone tell me who is my father?


Criminal Identification and Forensics

(DNA isolated from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared )


Diagnosis of Inherited Disorders and developing cure

(diagnose inherited disorders in both prenatal and newborn babies and by studying the DNA fingerprints of relatives who have a history of some particular disorder identify DNA patterns associated with the disease)

Study of Evolution(Find out relationship between various

races of human beings and study of organisms facing danger of extinction)

DNA Fingerprinting (AT A GLANCE) DNA sections with repeating sequences are called VNTRs and

are used in DNA fingerprinting. No DNA fingerprint test can prove defendant's guilt, but a

match can establish probability. A fingerprint begins with a sample of tissue such as blood,

skin, or semen. Fingerprinting can also be used to determine paternity and to

identify victims of disasters or war. It was developed in 1984 by Alec. J. Jeffrey. N……….? Gel electrophoresis separates the DNA fragments by size, as

the smaller pieces move faster through the gel. E……………? Restriction enzymes break DNA into more manageable sizes

for fingerprinting. PCR technique is used to amplify tiny amount of DNA. R………..? Indian government funded the Centre for DNA Fingerprinting and

Diagnostics (CDFD). N………….? T……………?

HOTS Questions1. HGP provides detailed information about genetic

constitution of an individual, then why DNA fingerprinting is used in criminal cases and paternity disputes?

2.VNTR does not code for any protein yet they are important in DNA fingerprinting?

3. What is DNA polymorphism?

4. If insufficient amount of DNA found from a crime scene, how amount of DNA could be increases?

5. Differentiate repetitive DNA and satellite DNA.

6. During investigations of a criminal case it was found that DNA fingerprints of two suspicious individuals was exactly similar. How it can be possible?

REFERENCESNCERT Text book of Biology (XII)

Comprehensive Biology (XII)

Truman’s elementary Biology +1

Madhuban a text book of Biology part 2

Modern’s abc of Biology XII

Internet

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