Policie České republiky – Kriminalistický ústav
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Forensic Genetics
Forensic genetics examines biological evidence found at the scene of crime and its aim is to unambiguously identify its source. DNA is contained in all cells (except erythrocytes), tissues and organs and it remains invariable the whole life. A profile, unique to every individual, is determined from DNA for identification purposes.
The following are analysed most often:
- blood, sperm, saliva, hair, skin flakes, bones,
- swabs from surfaces the perpetrator might have touched.
1. Chromosome
2. Sample collection
The Police of the Czech Republic carries out so called “identification DNA analysis” meaning than only non-coding DNA sequences, which do not contain any information on the individual´s appearance or their predisposition to certain illnesses or diseases, are tested.
3. Sample preparation
DNA profiles can be digitalized, mutually compared and kept in the Forensic DNA Database. It contains DNA profiles of persons (charged, convicted, unknown corpses) and DNA profiles from evidence from the crime scenes of cold cases and elimination samples. Every line of the genetic profile represents a particular non-coding DNA sequence. Persons differ from each other by the length of the sequence. Analysing DNA, the expert determines the length and expresses it as a number. Every DNA sequence is, in a human body, in two copies of which one comes from mother and the other from father. From a sample of the DNA identification profile, it is possible to tell only the sex of the individual (XX – woman, XY – man).
Evidence from a CS – DNA analysis – DNA profile determination
A DNA profile determined from the evidence found at the crime scene is compared to the DNA profiles in a database or to the DNA profiles of suspects that are thought to be relevant by the Criminal Police:
if a positive match is found, the biological material from the crime scene is matched to a particular person or to a piece of evidence from another crime,
if there is no match, the determined DNA profile is saved in the database.
Special analyses:
mitochondrial DNA – maternally inherited. Mother and all her children have the same mitochondrial DNA. This type of analysis is usually used to examine older and degraded material.
Y-chromosome – paternally inherited. Father and all his male children have the same Y-chromosome. The analysis is most often used in cases of rape or as an additional examination to detect affinity of unknown remains discoveries.