Chromosomes
Structures in the cell nucleus which contain hereditary information. A person possesses 2 x 23 chromosomes in all cells except germ cells. Schematic representation of chromosomes with the 16 markers used at the Confidence laboratory
DEFINITION OF TERMS
dNTPs
Desoxynucleosidtriphosphates these are the building blocks of the DNA. There are four different nucleotides: Adenin, Thymin, Cytosin and Guanin.
PCR
The Polymerase Chain Reaction is a method for amplification of DNA-sequences using primers that bind to the flanking sequences of the STR-sequences. The multiplex PCR allows the co-amplification of 16 loci simultaneously. (see picture)
The reaction is performed in 20 to 28 thermal cycles. In this way approximately one million copies of the DNA fragments are produced.
- First step: Denaturing of the double-stranded DNA at 94°C.
- Second step: Specific Annealing of the Primers on the complementary single-stranded DNA at 60°C.
- Third step: Chain Extension. This is the elongation of the primer by the heat-resistant enzyme called Taq-DNA-Polymerase at 70°C.
Primers
These are special sequences designed to bind to the regions on the DNA which are relevant to the analysis.
STRs - Short Tandem Repeats:
Short Tandem Repeats are repeating units of 3 to 7 base-pairs in Introns of the DNA. They serve as micro-satellites for the DNA-analysis. Comparisons between persons can be done because they are highly polymorphic and vary greatly through the population. This is why they are unique to each individual person. Only the flanking regions to which the primers bind are constant.
Taq-Polymerase
DNA Polymerase is a thermostable enzyme that was isolated for the first time from the bacterium Thermophilus aquaticus taken from hot water springs or geysers.
It replicates DNA at 74°C and catalyses the polymerisation of nucleotides into duplex DNA in the 5' to 3' direction (Primer extension reaction).