Transcript Forensic Biology by Richard Li - Fayetteville State University

Chapter 17: Variable-Number Tandem
Repeats Profiling
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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
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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
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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
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Restriction Endonuclease Digestion
 HinfI
 HaeIII
 PstI
 Analytic Gel
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Southern Transferring & Hybridization
 Southern Blotting
 Sir Edwin Southern, Mid-1970’s
 Transfer DNA to a filter so it can be detected with a probe
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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
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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”
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Factors affecting RFLP results:
 DNA degradation
 Partial restriction digestion
 Star activity
 Point mutations
 Electrophoresis and Blotting Artifacts
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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
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