The truth encoded in the genome

Differences in the DNA sequence are a unique signature, which in forensic science is often compared to the fingerprint. DNA variability arises due to various mechanisms and shows very large variations in scale. The smallest differences may concern individual methyl groups attached to cytosines, the largest ones include fragments with a length of millions of base pairs. During life, differences in the methylation pattern will also increase in DNA of monozygotic twins. Some of the differences that we observe in the DNA sequence affect the diversity of phenotypic traits. The genome is one of the most fascinating instructions that scientists try hard to get to know from when it became clear that the DNA contains all the necessary information needed for the life of a single cell and the entire organism. The information contained in the DNA is useful for identifying people with an undetermined identity. These investigations are conducted by forensic genetics.

Forensic genetics

can be defined as an application of genetic methods for more effective law enforcement. Modern forensic genetics has developed good methods for examining biological traces and samples that allow identifying people with an undetermined identity. As identification markers, microsatellite sequences are most commonly used. Evidence from DNA testing is valued by the justice system because of its high objectivity, reliability and high value, which is documented by the relevant statistical calculations. Therefore, the result of a DNA testing often strongly influences the verdict in court proceedings. 

DNA evidence

DNA markers used for human identification can be classified according to the type of variation and the type of inheritance. The most commonly used type of molecular marker is microsatellite DNA known in forensic genetics as STR polymorphism. The STR sequences are present in nuclear DNA, both on autosomal chromosomes and on sex chromosomes. The single nucleotide polymorphism (SNP) may also be useful for human identification. It represents the most common type of polymorphism in the human genome, also present in mitochondrial DNA. Markers tested in forensic DNA laboratories are inherited from both parents (autosomal), from father (Y chromosome), from mother (mitochondrial DNA) or in a complex way (X chromosome). Each of these types of marker may be useful depending on the context of the case. 

DNA-based phenotype prediction 

The further development of DNA analysis methods used at the investigation stage seems particularly exciting. These methods do not provide evidence for the court, but they can be particularly useful when the suspects were not selected during the investigation or the investigative hypotheses turned out to be wrong. In such a case standard human identification markers are useless but the biological traces can still be explored in the purpose to deliver the investigative leads. Gender, biogeographic ancestry, physical appearance and age of the unknown person may be relevant to describe a perpetrator of the crime. Such predictive DNA analysis in forensic science requires the analysis of multiple DNA variants. The current DNA phenotyping methods allow narrowing the number of potential suspects, and in the future they may allow direct identification of the criminal who left a biological trace.
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