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Lecture 15

Anthropology 2235A/B Lecture Notes - Lecture 15: Zygosity, Combined Dna Index System, Missing Person


Department
Anthropology
Course Code
ANTH 2235A/B
Professor
Eldon Molto
Lecture
15

Page:
of 2
Lecture 15 Key Developments in DNA Post RFLP
RFLP was time consuming and required considerable amounts of DNA to
be used
1984 - New technology the Polymerase Chain Reaction (PCR - the DNA
Xerox machine) allowed for smaller amounts of DNA (usually found at
crime scenes) to be amplified thereby preserving the sample
In 1991 Edwards writes first paper on new technique called Short Tandem
Repeats, which unlike RFLP could be adapted to the new PCR
technology!
Single Nucleotide Polymorphisms
Note on Taq Polymerase
o Taq polymerase is a heat tolerant enzyme that is derived from the
thermophilic bacteruium Thermus aquaticus first isolated from a
oceanic thermal vent by Thomas Brock in the 1980s! This enzyme
must be heat tolerant because heat-fragile enzymes would have to
be replaced after every step. Our enzymes only operant at body
temperature
PCR Reaction
o To multiply a DNA molecule with PCR requires:
Target DNA molecule
Primers
DNA polymerase that directs replication
Nucleotides (4 bases)
o Steps involved in PCR
High heat to separate the double helix (denaturing)
Cooling to allow primer binding (anneling)
Slight warming to allow polymerase to bind bases to the
target (extension)
STR Nomenclature
o If a marker falls within a gene (exon) the gene name is used e.g.
the STR TH01 is from the human tyrosine hydroxylase gene
located on chromosome 11, the ’01’ portion of this STR comes from
the fact that the repeat region in question is located within intron
(non-coding) 1 of the gene
o DNA markers that fall outside of the gene regions may be
designated by their chromosomal position (e.g. D5S818)
D stands for DNA
5 for chromosome 5
S stands for single copy sequence - 818 indicates the order
in which the marker was discovered (818th locus described
on chromosome 5)
DNA Databanks and Data Bases
o The fingerprint experience in the 1970s (AFIS) laid the foundation
for the development of DNA (STR) databanks and bases in order to
compare suspects with crime scene evidence
o The US launched CODIS in 1998
o This would require proper legislation to collect DNA samples (under
487 in the Canadian constitution)
o What is a DNA Databank?
Repository of forensic DNA profiles
Invariably includes:
Index of casework evidence profiles (crime scene
index)
Index of comparison profiles from offenders
(convicted offender index)
Some will also include missing person profiles
o PCR Problems with STRs
1. Contamination (low copy DNA) and the Locard Principle
contamination from many sources (e.g. bacteria DNA
investigators and lab techs) how do we get around some of
these problems problem?,
2. Degradation largest DNA will get amped
3. Sunlight is the biggest problem, we sue UV to decouple
DNA
4. Inhibitors many human, soil, calcium etc (our extraction
protocols focus on the inhibitor problem
5. Allelic Dropout and null alleles (failure to amplify one of
the two alleles present in a heterozygote)