Genetic identification in the scope of the biological criminalistics
The complexity of this expertise is in the diveristy of samples received for analysis (blood, semen, hair), and being sometimes very little degraded genetic material. In the implementation of this skill are collected traces at the site of the crime, the victim (mainly for sexual assault) and in the garments of the victim and / or the suspect, and subsequently sent to laboratories in order to study the DNA.
DNA Study
The interest in forensic expertise requires the extraction of DNA (acid Desoxirribonucleico) of nucleated cells and then using the PCR (Polymerase Chain Reaction), the amplification of DNA sequences, using commercial kits that allow, simultaneously to analyse several DNA polymorphisms. The main DNA polymorphisms are studied STR (Short Tandem Repetas) autossómicos, the Y chromosome and cromossomaX. When it comes to samples with small quantities of degraded genetic material, proceed the analysis of the control of mitochondrial DNA region, for sequencing. Currently, there are other genetic markers that can be used in the study of "difficult samples", as the SNP (Single Nucleotide Polymorphisms), the MiniSTR and analysis LCN (Low Cpy Number).
The final part of consites of the analysis of results.For this to be possible, in addition to determining the genetic profile of the biological sample, you have to get the genetic profile of a sample as a reference taken from the suspect for comparison.
After conduction of this analysis is produced a final report in which, among other things, will contain the conclusions that include the probability of matching results, in the case of identical genetic profiles being listed.
Individual genetic identification
Sometimes, the only traces that can be withdrawn from the scene of the crime are traces of contact of skin with any surface, being the most detected, fingerprints.
The analysis of these anatomic traces, traditionally lofoscópica today may have a completely different approach, through the determination of their genetic profile.
In a fingerprint present on the surface of an object may be adhering some nucleated cells that allow with, if appropriate treatment, the extraction of DNA and subsequent analysis. Indeed, several authors have shown that it is possible to obtain genetic profiles from residues of latent fingerprints, left by simple skin contact with certain surfaces, such as paper, knives, pens, ropes, wires and firearms.
Research on biological kinship
Experts in possession of cells of the criminals, analyze the DNA, identifying the fragments in the laboratory. Moreover, the police takes samples of blood from suspects of having committed that crime. When crossing the results of the examination of DNA of suspects with the result obtained from the criminal still unidentified, it is possible to reach identification.
Here is an interesting question:
If the identification of the perpetrator is given by the identification of fragments of DNA that he inherited both by the father and the mother, how can you be sure that the DNA analyzed is not of the of brother of the suspect?
Although they are brothers that does not mean that they have inherited exactly the same genetic baggage. A certain sperm carries snippets of DNA that are different from the father excerpts loaded by neighbouring sperm. The same can be said with regard to ova that the mother produces.
Therefore, the combinations of maternal and paternal DNA occurring in fertilizations producing each of the children are different. In conclusion each person is unique in the world with respect to its genetic composition, and the result provided by DNA testing shows a kind of molecular fingerprint that gives no room for doubt.
Curiosities...
With only a 1cm-dryer it is possible to extract DNA;
- Only the monozygotic twins have the same DNA; The dermatóglifos are lines formed by the crist on superficy of the skin;
- The dermatoglifos form in the third and fourth months of fetal life and emerge to the surface in the fifth month. During their lives,they only change in size, without changing its configuration. In cases ofphysical or chemical injury the crests regenerate to its original form.
This was the last post on genetics and forensic biology! I hope you have enjoyed it! Do not miss the next post that will be about the crime solved month to month!
Written by: Teresa Felgueiras
Translated by: Teresa Felgueiras
Bibliography:
http://www.angelfire.com/falcon/biologiaunip/identificacao_DNA.htm
A química na investigação policial
Pelas pontas dos dedos
A química na investigação policial
Pelas pontas dos dedos
No comments:
Post a Comment