99% of human DNA is identical between two individuals, however that 1% is a big enough difference in order to distinguish the identity of one person. DNA has to be collected first from the individual which may be in the form of semen, saliva, hair, and blood. DNA fingerprinting makes use of the difference in the remaining percent in order to determine similarities and differences between individuals.
In fact a sample having only 20 cells is enough to test the crime scene. This is due to the fact that PCR can be used to amplify the gene. Only 5 segments of DNA which are known to be highly variable amongst individuals are tested.
Restriction enzymes are used first to cut the DNA into fragments with sticky ends. These fragments are called restriction fragment length polymorphisms or RFLP for short. However, DNA is not only composed of coding sequences, there are also non-coding sequences.
Non-coding DNA sequences are often repeated throughout the genome which gives rise to variable number tandem repeats or VNTRs. The actual number of repeats in the VNTRs can serve as a clue to identify the suspect.
Using gel electrophoresis, the fragments are arranged according to their sizes. Once electric potential is ran across the sample, the negatively charged RFLPs moved toward the positive charge which means that the smaller fragments move farther across. This is possible due to the alkaline solution which breaks the hydrogen bonds of the strands of DNA. Moisture is then absorbed through the gel through using nylon and thin paper towels and then DNA is transferred to the nylon. This process is called blotting.
Radioactive probes then get washed over the nylon surface which will eventually join DNA fragments having the same composition. The final step in making a genetic fingerprint is placing a photographic film on top. The probes will then automatically leave marks on the film wherever they attach to the RFLP. We can then compare these distinct patterns with other fingerprints to decipher the similarity and differences of the individuals.
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Aside from identifying the suspects of a committed crime using DNA analysis, DNA fingerprinting is also used to track heredity. Bands of parents and offspring often exhibit the probability of relatedness. If the similarities are quite big, then both of the samples are most probably related.
DNA fingerprinting can also be used to predict future health. Diseases can be tracked down to know whether the disease can be hereditary and therefore aid awareness of the individual affected.
Furthermore, DNA fingerprinting aids in the identification of a person, say, a bone sample to test whether or not an individual has actually died.
However, one drawback DNA fingerprinting poses is the fact that twins have the same DNA sequence and therefore cannot be identified. Therefore skeptics say that there is actually no sound proof that DNA sequence between unique individuals is also unique. Furthermore, contamination may result in the invalidity of the testing procedure.
Criminals may also use foreign DNA to blame the crime to another person. In this procedure, criminals plant fake DNA to the crime scene to render them innocent.
In the Philippines, the use of DNA forensics is stressed on two rape cases, one occurring in Cavite by a fisherman and the other another rape case which lead to pregnancy. Gerrico Samartino, the fisherman who raped a 9 year old girl in Cavite was convicted with the heavy evidence of rape with homicide using DNA forensics. The semen found on the girl’s genitals matched Samartino’s DNA.
As for the other rape case, Victoriano Paras, was deemed inoocent due to the negative results of the paternity testing. In both cases, the validity of the allegations caused a faster and more truthful process for justice. Samartino was convicted in just a matter of 12 months while the latter in just a matter of two weeks.
Most of the analyses in DNA fingerprinting is used in high profile case studies against complainants.
Most recently, forensics was used in the case of Ted Failon, TV Patrol newscaster, in the case of allegedly killing his wife.
