What is forensic DNA analysis

Forensic molecular genetics is essentially concerned with the individual assignment based on the so-called genetic fingerprint. DNA occurs in the cell nucleus and in certain cell organelles, the so-called mitochondria.

The core DNA is the carrier of all genetic information. The DNA molecule contains four bases - adenine, cytosine, guanine, thymine - which in pairs - always adenine and thymine as well as cytosine and guanine - are attached to each other and form a double strand. The sequence of the complementary strand always results from the sequence (base sequence) of the primary strand.

Only 2-3% of the core DNA contains so-called coding (readable) sequences as hereditary information. The majority consists of non-coding sequences that are highly individual. Forensically relevant DNA techniques concentrate on these highly individual, non-coding DNA segments. So-called STRs (short tandem repeats), which have a DNA length polymorphism, are mostly used for forensic purposes. Such polymorphisms are of short sequence length and thus represent an advantage in the study of degraded material.

Most STR systems are so-called autosomal systems, i.e. they are located on the autosomes. Of these chromosomes, humans have a double set, a single set from the father and a single set from the mother. A human therefore has two alleles in every STR system, one paternal and one maternal. The alleles are named according to the number of repetitions of the basic motif.