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Forensic genetics 2 (DNA profiling (DNA analysis performed in forensics…
Forensic genetics 2
DNA profiling
- Why to test DNA?
Identification with high probability
low costs of analysis
We always leave DNA around
High stability of DNA
Extremely high sensitivity
- 99,9% of human DNA is common between individuals
- 0,01% (0.3%) DNA of every man is different and unique except for monozygotic twins.
- DNA loci used for forensic genetics are highly polymorphic
- Steps of Forensic DNA Typing:
Revealing, Tissue identification, DNA extraction, DNA quantification, Genotyping, Interpretation, Testimony
- Two types of DNA polymorphism:
DNA length polymorphism (tandem repeats) (nuclear DNA)
DNA sequence polymorphism (single nucleotide polymorphism – SNP) (mtDNA and nuclear)
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- Three Possible Outcomes:
• Match – STR profiles have the same genotypes.
• Exclusion (Non-match) – profile differences.
• Inconclusive –DNA sample is LCN type, degraded or complicated DNA mixtures are present (insufficient information exists to support any conclusion).
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Gender determination
- Amelogenin gene: Homogeneity of Amelogenin from X and Y chromosomes is over 94%.
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-Problems to overcome in profiles analysis
-Low copy number (LCN) DNA,
-Degraded DNA,
-DNA mixtures: A mixture of DNA from two persons is represented by up to 4 alleles in each locus, from three persons – up to 6 alleles etc.