Forensic DNA Profiling Forensic DNA profiling ABO blood

Forensic DNA Profiling

Forensic DNA profiling § ABO blood typing § Lacks power of discrimination § RFLP analysis using minisatellite probes § High power of discrimination § Laborious § STR analysis § PCR-based § Highly discriminating § Fast § mt DNA analysis § PCR-based § Slow due to the need for sequencing

STR analysis § Short tandem repeats (STRs) § Short nucleotide sequences that are repeated in tandem § Eg: CAGCAG or (CAG)n § Composed of different numbers of repeating units in individuals and § Compares the lengths of STR sequences at specific sites in the genome

CODIS loci § Combined DNA index system § Typically analyzes 13 different STR sites and the AMEL (amylogenin) locus § CODIS profile has 26 numbers, since each locus has two alleles § The probability of match between any two random people is 1 in 575 trillion § Exception: Identical twins

CODIS Loci

Figure 12. 14 A Two representative STR sites from crime scene DNA samples STR site 1 STR site 2 Crime scene DNA The number of short tandem repeats match Suspect’s DNA The number of short tandem repeats do not match

Figure 12. 14 B DNA profiles generated from two STR loci Crime scene DNA Suspect’s DNA Longer STR fragments Shorter STR fragments

STR analysis ◦ All loci amplified at once: each primer set is labeled with a different fluorescent dye ◦ Fragments separated using capillary electrophoresis and read with a laser beam. ◦ No gel electrophoresis involved