Classic fingerprinting - Subject to intrepretation Samples can be hard to get Due to the “uniform nature of DNA” and the variability of genes, fingerprint identification can be done
Classic fingerprinting can be argued/debated DNA can’t be denied
The term DNA Fingerprinting was first mentioned by Alec Jeffreys.
A technique by scientists to distinguish individuals of the same species by using only samples of DNA.
Polymorphic DNA - Regions that vary from person to person like VNTRs or STRs
Scientists scan this to create a DNA profile (Fingerprint) of that individual.
VNTRs & STRs as Molecular Markers in Forensics
Polymorphisms in chromosomal DNA may arise from a variable number of tandem repeats (VNTR) or short tandem repeats (STR). VNTRs are minisatellite. STRs are also called microsattelites
VNTRs or STRs are short sequenes of nucleotides repeated on after another (in tandem) and located at several locations in the genome.
The number of repeat units in any location in the genome varies for each person but is unique for each person. Therefore they can server as a molecular “fingerprint.”
A VNTR is a region that is variably composed of 15-70 base pair sequence tandemly arranged head to tail, typically repeated 5-100 times.
An STR is similar to a VNTR except it’s only repeated in 2-4 nucleotides in length
Nucleotide - A, B, C, G. A base pair attached to a rhybose sugar.
Use of RFLP & Southern Blotting in DNA Fingerprinting
- Isolate chromosomal DNA from a sample of cells to compare
- Use restriction enzyme to cut dna
- separate the dna fragments by gel elctrophonesis
- Transfer bands to nitrocellulose
- Denature the DNA and add probe. Allow probe to hybridize and wash away excess probe
- Expose the filter to photographic film and compare results
RFLP of VNTRs & STRs
Number of tandem repeats of a sequence is highly variable within a population
Cleavage of VNTRs or STRs by restriction enzymes yields fragments that vary in length depending on how many repeated segments are containsin fragment
By examining several different VNTRs or STRs from the same individual investigators obtain a unique DNA fingerprints for that individual which is unlike that of any other person (except for an identical twin).
Advances in Molecular Biology & Forensics
Advancments have improved diagnostic sensitivity, accuracy, and validity of forensic science. Especially in human and non-human identification.
Automated fingerprinting, cloud computing, and facial identification, are revolutionizing modern forensics.
Some companies are developing rapid DNA analysis tech to address growing needs for DNA analysis in forensics and biometrics.
Next Generation Sequencing of Microhaplotype Loci
Microhaplotype loci (microhaps, MHs) are molecular marks of less than 300 nucleotides. Defined by two ore more closely linked SNPs associated in multiple allelic combinations.
Massively parallel Sequncing (MPS) allows the sequencing of both parental haplotypes at each of the many multiplexed loci.
Loci is the location of a gene.
Value in individual identification, ancestry inference & determination of family/clan relationships. May be used in person identification and medical diagnostic applications. Not restricted to just humans.
MPS will take from multiple places of DNA to sequence.
VNTRs & STRs as Molecular Markers in Forensics
Several STR and VNTR loci have been identified and are useful for fingerprint analysis such as in forensics and paternity case. These polymorphisms are simply marks, which, have no known effect (in most cases) on the structure, function, or rate of production of any specific protein.
Any match between crime scene DNA and a suspect’s DNA at a single locus (singular loci) does not prove guilt, nor does it rule out innocence. Therefore, multiple loci are tested and evaluated.
The number of repeats differ among alleles. An analysis of 8 to 16 STRs is usually sufficient for a statistically valid match.
Matching about 8 to 16 polymorphisms (using multiplexed PCR for polymorphic STRs or primer extensions for SNPs) from DNA at the crime scene with DNA from a suspect. These products are compared to the products obtained from the unknown sample, and matches, or nonmatches, can be determined.
DNA Typing
You look for matches (based on sequence or on numbers of small repeating units of DNA sequence) at a number of different locations on a person’s genomes
It is necessary for all appropriate controls to be run, including samples from the victim’s DNA as well as the suspect’s DNA.
Several matches must be found to be confident beyond a reasonable doubt. That the right person is identified.
DNA fingerprint of Identical Twins
There is an extremely small chance that another person has the same DNA profile for a particular set of regions: identical twins would have similar DNA fingerprints.
Use of DNA in Forensic Identification
Identify potential suspects whose DNA might match evidence left at the crime scene
Exonerate persons wrongly accused of crimes
Identify crime and disaster victims
Establish paternity and other family relationships
Inheritance Cases
Immigration Cases
Identify endangered and protected species as an aid to wildlife officials
Detect bacteria and other organisms that may pollute air, water, soil, and food
Match organ donors with recipients in transplant programs
Determine pedigree of plands, and live stock breeds
Authenticate consumables such as wine
First Practical Tests of DNA Fingerprinting
1983-1985: A two year struggle by Christiana Sarbah and her son, Andrew, to prove to the Home Office in Englad that they were indeed, mother and son.
1986: The Pitchfork murder case: the origins of DNA profiling.
DNA Fingerprinting: Solving a Rape/Murder Case
DNA samples obtained from three suspects & Victim in a rape and murder case.
PCR used to amplify the NTRs because victim’s sample size is small.
A number of different restriction enzymes and probes can be used for more positive identification.
If other restriction enyzymes and probes corroborate finding from VTNR pattern match DNA to semen obtained from victim. may identify by DNA fingerprinting the suspect as the rapist/murderer.
Multiplex PCR in Identifying an Unknown Rhinoceros Horn Sample
A rapid rhino indetification test, using species-specific primers within the cytochrome b gene multiplexed in a single reaction.
Identification is based on the length of the resultant amplicon.
This multiplex PCR assay can provide a presumptive species identification result in less than 24 hours.
Mitochondrial DNA (mtDNA) in Forensics
Maternal inheritance and polymorphic nature of mtDNA have enabled investigators to identify war casualties, missing persons, and individuals involved in mass criminal cases and disasters.
mtDNA is extremely valuable in the investigation o fcases taht have not been solved for many years
Comparing mtDNA profile of unidentified remaints with the profile of a potential maternal relative can be important technique in missing person investigations
Mitochondrial DNA analysis in the Identification of Human Remains
Y-Chromosome Analysis
Y-chromosome passed directly from fater to son. Valuable for: Analysis of genetic markers on the Y chromsome Tracing relationships among males Analyzing biological evidence involving multiple male contributors.
Combined DNA Index System (CODIS)
In the US a core set of 13 STR markers is used to generate a nationwide DNA database called the FBI combined DNA Index System.
The CODIS and similar DNA databses have successfully linked DNA profiles from repeat offenders and evidence from crime scene.
DNA Databanking
UK - Nationa DNA Database Suspect Profiling Database contains DNA profiles of individuals:
- suspected of
- Charged with or
- about to be reported for,
- a recordable defense
US - National DNA Indexing System Convicted offender profiling
CODIS uses two indexes
Convicted Offender Index contains DNA profiles of individuals convicted of felony sex offenses (and other violent crimes).
The forensic index system contains DNA profiles developed from crime scene evidence
Potential benefits of DNA databanking arrestees
Many major crimes involve people who also have committed minor offenses.
Innocent people are often incarcerted for crimes they did not commit. If samples had been taken at the time of arrest, theese individual may have been excluded early in the investigation Abiliity to compare other cases against the arrested person’s DNA profile, just as with fingerprints Savings in Investigation, proescution, and incarcartion. e.g. John Mark Karr /JonBenét Ramsey Case.
Ethical, Legal, and Social Concerns about DNA Databnking
- Privacy
- Who is chosen for sampling
- Practicality
Misc.
Sanger(?) from the UK. Made Sanger(?) sequencing. A way to sequence all of the DNA to know the exact sequence of DNA. Basically,
A always goes with T C always goes with H
Polymorphism - Many forms