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Term Paper on DNA Fingerprinting

Term Paper # 1. Introduction to DNA Fingerprinting:

Identification and characterization of individuals is carried out at different levels. These can be social, physical or biological. The biological identity means phenotypic and genotypic markers. Most commonly used biological markers for individual identification include blood groups, serum proteins, enzymes, etc.

These markers have proved useful but they are limited in number and their degree of variation. So these cannot be used in precise identification of specific individual. Most of the genomes of animals and plants cannot vary greatly between individuals because it has an essential coding function.


In non-coding regions this requirement does not exist and the DNA sequence can accommodate changes. One change, which does occur, is the tandem repetition of DNA sequences. The discovery of hyper variable repeats (HVR) in human DNA has created a powerful new class of genetic markers, which promise to revolutionize forensic biology, and opened new vistas in animal and plant sciences.

The HVR, also referred to as mini-satellites or variable number of tandem repeats (VNTRs), consists of core tandem repeats of a short nucleotide sequence about 15-30 base pairs in length.

They are hyper-variable because the number of tandem repeats, and hence the length of DNA in that region, varies considerably in the general population. DNA probes have been isolated which detect families of these HVR located at many different chromo­somal loci. The probability that two unrelated individuals have identical lengths of DNA at a particular HVR is very low.

However, the probes that have been developed to detect 30-40 different HVR simultaneously, so the probability that all of these are the same length in both individuals becomes vanishingly small. The complex banding pattern obtained when southern blots of DNA are hybridized with these probes is therefore individual specific, and is referred to as a DNA fingerprint.


DNA identification analysis, identity testing, profiling, finger-printing, and typing or genotyping all refer to the same phenomenon of characterization of one or more rare features of an individual’s genome or hereditary make up by developing DNA fragment band (alleles) patterns. If sufficient number of different size bands is analyzed, the resultant bar code profile will be unique for each individual except identical twins.

The bands of DNA profile are inherited in a simple Mendelian fashion and behave as co-dominants; the maternal and paternal derived variants at any given locus are detectable. DNA fingerprinting is considered most important among various genome markers and like restriction enzyme length polymorphism there being genetic loci at which nearly every individual is unique and different.

In such a case an offspring would inherit one or the other of the allelic status of each marker from each parent. Another offspring of the same parents would again inherit markers from the parents, but it would be different set. Thus, some markers in the two off-springs would be same and others would be different.

On the other hand, two unrelated individuals would possess virtually no markers in common. Proponents of DNA fingerprinting claim that the probability of two DNA samples matching by chance is very low, somewhere between 10-6 to 10-15.


The principle of individual uniqueness and identical DNA structure within all tissues of the same body provides the basis for DNA fingerprinting. Jeffreys and his colleagues developed DNA fingerprint system utilizing the nature of hyper-variability of these regions in human beings.

The advent of DNA fingerprint technique has revolutionized the identification of any biological specimen by dramatically reducing the number of tests required, yet radically increasing the power of identification precisely. Impact of DNA fingerprinting technique on science, law and politics has been dramatic. Recently this technology has been found to have many applications in livestock, primates, birds and other species.

Term Paper # 2. Genetic Basis of DNA Fingerprinting:

The four bases of DNA are organized in different ways in DNA sequence, which is quite variable in individuals. The repetitive sequences generally comprise 2-250 bp of a specific sequence, which is typically repeated between a few to several thousand times. The resulting multiplicity of lengths of these segments is called length polymorphism (HVR or VNTR).


The development of different probes provided tools for the observation of numerous hybridization signals and thus a large number of bands (DNA fingerprinting). Using appropriate stringency hybridization conditions, highly polymorphic DNA bands scattered throughout the entire genome of humans and animals can be detected.

Term Paper # 3. Methodology of DNA Fingerprinting:

The methods used in obtaining DNA fingerprinting are conventional techniques of molecular biology. Each technique has many alternative protocols; however, one should standardize protocols suitable to the conditions and facilities available in the laboratory.

The general outline of the procedure is as follows:


1. Isolation of DNA:

DNA can be isolated from any tissues containing nucleated cells. However, in animals quite commonly used sources of DNA are blood, semen, etc. Leukocytes or sperms from these tissues are lysed using specific buffers and subjected to proteinase-K digestion. Digested proteins are precipitated and DNA is removed with the help of repeated phenol- chloroform-isoamly alcohol extraction technique. DNA is finally precipitated using isopropyl alcohol. Subsequently, its quality and quantity should be checked.

2. Digestion of DNA by Restriction Endonuclease:

About 5-10 g DNA is sufficient to get good quality fingerprinting. Commonly used enzymes are EcoR 1, Hae III, Alu 1, etc. A typical reaction mixture for DNA digestion contains DNA, enzyme, buffer specific for each enzyme, BSA, distilled water. The reaction mixture is incubated overnight at a specific temperature. The digestion is stopped by heating or addition of EDTA.


3. Electrophoretic Separation of Different Fragments:

The digested DNA is an admixture of DNA fragments of various sizes. These segments are separated according to their sizes by electrophoresis. Appropriate DNA size markers are also used on the side lanes of DNA samples.

4. Transfer of DNA on Nylon Membrane:

The size separated DNA fragments should be transferred to a solid surface usually a nitrocellulose or nylon membrane for further use by adopting a method known as southern transfer. Transfer can be accomplished by using either capillary or vacuum transfer method.

5. Probe Labeling:

A DNA probe is a stretch of DNA fragment, which is complementary to target sequences in the genome. In DNA fingerprinting the probe will be complementary to repeating units of DNA or also known as satellite DNA which falls under different categories depending on size of the repeating unit. The probes are labeled with 32P radioactive labeled nucleotides.

6. Hybridization:

The labeled probe DNA should be hybridized with the complementary sequences located on the nylon membrane for the detection of position of the latter. It involves incubation of nylon membrane with the labeled probe in proper hybridization solution at appropriate temperature.

7. Autoradiography:

It involves alignment of hybridized nylon membrane with an X-ray film in a cassette followed by a specific duration of incubation at a low temperature. The X-ray film alter its development shows lanes with bands or multiple number of bands that look like bar codes otherwise known as DNA fingerprints.

8. Analysis and Interpretation of Band Patterns:

It is done by comparison of position of bands and by band sharing tendency using various computer software’s.

Different areas of animal science where DNA fingerprinting has a great potential are:

1. Individual identification,

2. Pedigree analysis and parentage verification,

3. Conservation of genetic resourced,

4. Zygosity testing,

5. Demographic studies,

6. Quality control of cell banks,

7. Sex determination,

8. Detection of loci controlling quantitative traits or disease resistance,

9. Pathogen identification,

10. Identification of carcass of tissues,

11. Detection of somatic mutations of cancer, and

12. Taxonomic tool.