ΕUROPEAN CENTER FOR GENETICS & DNA IDENTIFICATION

ΙΑΤΡΟΔΙΚΑΣΤΙΚΑ

GENETIC PROFILING AND CLINICAL APPLICATIONS

A genetic fingerprint is the genetic identity of an individual and consists of characteristic blocks of the genetic material that are unique to each person.

In the field of genetic profiling there are 2 kinds of samples:

-reference samples, which correspond to the DNA of known individuals that are linked to their genetic profiles = «DNA reference profile». The most desirable method of a reference sample collection is that of a buccal swab or blood sample, as this reduces the possibility of contamination.
- unknown samples
, which correspond to stains (blood, sperm, saliva, hair, bowel etc) that have been collected during investigations and belong to an unknown person = «unidentified DNA profile »

The genetic comparison of 2 samples, «reference DNA samples» and «unidentified DNA samples», which corresponds to their identification is based on 3 principles:

1. The unique genetic profile of each individual (only monozygotic twins are genetically identical); although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different to distinguish one individual from another.
2.
The DNA of an individual is exactly the same in each and every cell, allowing for the comparison of , for example, DNA extracted from sperm to DNA extracted from blood, hair etc.
3.
The unique combination of genetic material (alleles) in a new cell, so the genetic material of an individual is derived from the genetic material of both their parents is roughly equal in amount, which allows parental testing to be performed.

30/01/2010 17:00

THE NEW HORIZONS OF DNA

Evolution: With the passing of time, DNA analysis techniques are improving all the time ... For this reason the role of the investigator is becoming increasingly important.

To get a good genetic fingerprint from nuclear DNA, one must first obtain evidence from a sufficient number of «target DNA sequences». In other words: a sufficient quantity of small DNA segments that allow for its multiplication (amplification). This latter process will allow for later identification of genetic characteristics of the sample.

Stronger and stronger

Indeed, the acquisition of a genetic footprint mainly depends on the quantity and the quality of the DNA which could be isolated from trace/evidence. The concept of quantity is directly derived from the general nature of the sample. We believe that we require at least six «target DNA sequences»- i.e. the DNA of three cells – in order to obtain a genetic fingerprint. On the other hand, a decomposed corpse will give abundant but poor quality (degraded) genetic material, not allowing for the amplification of DNA. Another quality problem is to obtain a mixed genetic fingerprint, i.e. a mixture of many different sources of DNA that also complicates the interpretation of the DNA profile...

But genetics is a science that is constantly evolving: the use of new genetic markers that allow for the amplification of even smaller (and more degraded) DNA segments opens up new horizons for investigations. In our labs we have successfully managed to draw the DNA of a person who threw a stone or the DNA of an arsonist who handled a petrol cap...

 

In future, all that could be used as simple practice for surveys!

 

New questions

All these scientific advances must certainly make the scientific community happy but at the same time we must be ready for them. The use of better techniques will definitely require more human thought.

By revealing and using ever smaller amounts of DNA there is an urgent need to question how the DNA was found there. For example, the trace of saliva found on a victim's clothing may well come from its perpetrator ... but also from a simple passenger who the victim spoke to on the road!

Let us not forget that a simple handshake can cause the exchange of cells.

The investigator can then be reassured: despite technical and scientific progress, his role is increasingly important...

30/01/2010 16:55

APPLICATION OF GENETIC FINGERPRINTING IN FORENSICS

In everyday applications, the field of Genetic Profiling needs to answer one particular question: « To whom does the biological specimen found at the crime scene belong? »

In order to answer that we need to compare the «unidentified DNA profile» to the «reference sample» i.e. the «reference DNA profile».

The analysis process has 3 main stages:
1. Extraction and analysis of the DNA samples
2. Analysis of the results to create an individual’s profile and comparison to another sample to determine if it is a match or not.
3. In the case of a genetic match then the 3rd step is applied in order to check (calculate) the statistical error.Comparison of the DNA analysis results to check if there is a match or not.


Α) Paternity Testing

A few years ago paternity testing was performed by ABO blood type typing. However this kind of method could accurately exclude paternity but couldn’t confirm a paternity match. Today using DNA profiling paternity can be calculated with a probability typically greater than 99.9%.Our genetic material has 2 alleles from each gene, one allele inherited from each parent. Therefore 50% of our genetic material comes from the mother and 50% from the biological father.
In case of a child’s genetic profile matches to the alleged father’s identity ,the probability of paternity is calculated using the paternity index (PI) that is a statistical measure of the likelihood of a biological relationship. (typically as high as 99.9999% and more).
The same method can also be applied not only for maternity testing ,but also for the identification of dead bodies when brothers/sisters are available.

 

Β) Forensics

i. Rapes:

Genetic profiling has been very useful in cases of sexual assaults. The molecular techniques that are applied today allow for the differential separation of vaginal epithelial cells from sperm cells in order to determine the profiles of the victim and the perpetrator. Therefore ,mixed profiles are more accurately identified.
In rape cases genetic fingerprints can be detected in different kind of specimens: underwear, clothes, tissues, condoms etc.

 
ii. Other crimes:

Any biological specimen can be detected and analyzed if there are enough cells: bloodstains, nasal secretions, sperm, saliva on cigarette butts, bottle necks or glasses and also in many others such as, toothbrushes, hair combs, gloves, chewing gum, fruit, food, forks and knifes etc.
In burglaries where weapons are involved DNA can be detected from the weapons, the bullets, the masks etc.

30/01/2010 16:49