Forensic Biology by Richard Li Chapter 17: Variable-Number Tandem Repeats Profiling Forensic Biology by Richard Li

Basics Human genome is abundant in tandem repeats Minisatellites- 1980 GC-rich core sequence Also called Variable-Number Tandem Repeats (VNTRs) Several base pairs to hundreds Genotype is defined by a particular number of tandem repeats at a given locus Forensic Biology by Richard Li

VNTR Loci Loci located far apart on the same chromosome or on different chromosomes used Population Match Probability (Pm) Lower Pm the less likely a match will occur between two randomly chosen people Pm 10⁻¹² Forensic Biology by Richard Li

Restriction Fragment-Length Polymorphism (RFLP) Genomic DNA preparation Restriction endonucleas digestion Agarose gel electrophoretic separation of the DNA fragments according to size Transfer of DNA fragments Hybridizing with locus specific probes Detecting locus specific bands by autoradiography or chemiluminescence Forensic Biology by Richard Li

Restriction Fragment-Length Polymorphism (RFLP) Restriction Endonuclease Digestion HinfI HaeIII PstI Analytic Gel Forensic Biology by Richard Li

Restriction Fragment-Length Polymorphism (RFLP) Southern Transferring & Hybridization Southern Blotting Sir Edwin Southern, Mid-1970’s Transfer DNA to a filter so it can be detected with a probe Forensic Biology by Richard Li

Restriction Fragment-Length Polymorphism (RFLP) Hybridization Multi-locus probes (MLP) Multiple VNTR loci simultaneously Sir Alec Jeffreys- 1984 DNA Fingerprinting Parentage cases Not useful in mixed samples, degraded samples or limited quantities of DNA Forensic Biology by Richard Li

Restriction Fragment-Length Polymorphism (RFLP) Hybridization Single-locus probes (SLP) Recognize a specific region of the genomic DNA at a VNTR locus DNA profile 1983-first used in criminal investigation in U.K. Bins Possible Conclusions: “Inclusion”, “Exclusion”, “No Conclusion” Forensic Biology by Richard Li

Restriction Fragment-Length Polymorphism (RFLP) Factors affecting RFLP results: DNA degradation Partial restriction digestion Star activity Point mutations Electrophoresis and Blotting Artifacts Forensic Biology by Richard Li

Amplified Fragment Length Polymorphisms (AFLP) Some VNTR loci have short alleles and are applicable to PCR amplification D1S80: 14-42 repeat units Requires less DNA and better with degraded samples Amelogenin typing Replaced with STR system in 1990’s Forensic Biology by Richard Li