DNA Fingerprinting Flashcards
Name three steps in preparing a DNA fingerprint
1) obtaining samples
2) extracting and quantifying the DNA
3) analysing the DNA
Forensic science
The intersection of law and science. Using scientific tests in the investigation of crimes.
VTNRs (variable number tandem repeats)
Repeated sequences of between 1 and 100 base pairs located in the the introns
Ideally DNA loci analysed should:
1) be highly polymorphic
2) be easy and cheap to characterise
3) give profiles that are simple to interpret
4) have a low mutational rate
DNA databases
A collection of DNA profiles from evidence found at unsolved crime scenes and from suspects and convicted criminals
DNA fingerprinting
A technique used to link biological samples from a crime scene to a suspect
Why would you collect DNA profiles in a database?
1) criminals tend to reoffend
2) the severity of crimes often increases
3) a small number of people are responsible for a large number of crimes
Reasons why some people consider DNA databases an invasion of privacy
- people are worried that insurance companies or potential employers will use them to identify genetic defects that might cost them money
- concerned with illegitimacy
Restriction endonucleases
Bacterial enzymes that cut at a specific DNA sequence
RFLPs
Variations among individuals which prevent restriction enzymes from cutting at specific base pairs
Locus
Target area on DNA fragment
2 main aims of DNA extraction
Maximise yield and maximise purity of DNA
Factors that determine method of DNA extraction
- type of biological sample
- speed
- automation
- cost
4 extraction methods commonly used in forensics labs
1) Chelex 100 resin
2) Silica-based extraction
3) Phenol-chloroform extraction
4) FTA paper
Principle by which Chelex 100 resin works
Resin has a high attraction for polyvalent ions (Mg2+). It will isolate the proteins at the bottom of the tube
Principle by which silica-based DNA extraction works
DNA bunds to silica or glass particles in 6MNaCl
Principle by which the phenol-chloroform method of DNA extraction works
Phenol denatures the proteins that, after centrifugation ions are found at the interface while DNA remains in the aqueous phase
Principle by which the FTA paper method of DNA extraction works
Cellular materials lysis on contact with the paper, DNA binds to the paper
What are the nucleated cells in bone matrix called?
Osteocytes
What are the nucleated cells in teeth called?
Odontoblasts and fibroblasts
5 standards used for DNA fingerprinting
1) relevancy test
2) the Frye standard
3) the Coppolino standard
4) the Marx standard
5) the Daubert standard
Relevancy test
Must be relevant to case
Frye standard
Technique used to gather evidence must be generally accepted by the scientific community
Coppolino standard
Allows a new/controversial technique if adequate foundation can be laid
Marx standard
Court must be able to understand and evaluate the evidence presented
Daubert standard
Requires pre-trial hearings for scientific evidence
Chain of custody
A list of all people who came into possession of an item of evidence
