Topic 14: Wildlife Forensic Analysis Flashcards
What is the mission of the forensic unit in Alberta?
Provide forensic investigative support to Fish and Wildlife officers in Alberta (and pro bono work in other districts)
Deal with non-enforcement based forensic work, with problem wildlife and wildlife found dead
Forensic research on the side
What is the law and science side of wildlife forensics?
LAW: illegal possession of wildlife, hunting without a license/ out of season, trafficking, wastage and commercialization of wildlife
SCIENCE: species identification (what), DNA matching (who), population assignment (where), post mortem analysis (how did it die?)
Why is DNA used?
Unique, plentiful, consistent between cell types, stable (works on trace evidence), nature of wildlife crimes
In most poaching cases, the perpetrators are interested in biological material
Tells us WHO, WHAT, and WHERE
How is DNA used to determine what species the material is?
DNA marker used has to be the same within species and different between species (mitochondrial gene is usually used), have this for mammals and birds, 160-200 bp fragment of rRNA mitochondrial gene
How is DNA used to determining which individual the material is from?
DNA MATCHING
DNA marker used has to be a region of DNA that is highly variable and likely to be different between individuals, ideally one marker with and infinite number of alleles but in reality use many highly variable markers so that any one individual is unlikely to share alleles across all markers
MICROSATELLITES (highly variable, no linkage, easily interpretable)
Di or Tetra nucleotide repeats
Compare alleles across many markers and must share all of them
What happens once you have a match of biological material to an individual via DNA matching?
Need to assess the significance of the results using random match probability.
RMP: the probability that a randomly chosen individual from the population will have the same genotype. For a multi-locus genotype, it is the product of genotype frequencies at each locus
Genotype frequencies found via HWE, but need to know the frequencies of different alleles in different populations
What are allele frequency databases?
Samples are collected opportunistically, but should be from mortalities, want to cover the range of species and/or distinct genetic groups, and test data for HWE, linkage disequilibrium and null alleles
What is involved in the population genetic analysis?
Investigate presence and magnitude of population genetic structure within the population, which influences how the population should be broken down
Once allele frequency databases are collected and analyzed, what can they be used to do? What are two conservative modifications that the forensic unit does and why?
They can be used to calculate and match stats
Two conservative modifications that the forensic unit makes to the standard HWE equations are to account for null alleles and rare/novel alleles
What is the solution to the fact that rare or novel alleles are sometimes not detected in populations?
Substitute the frequency of rare and novel alleles below a threshold with a minimum allele frequency when calculating match stats.
The use of a minimum allele frequency consistently produces a match stat in favour of the defendant, and is based on population size
What causes null alleles or allelic dropout?
Null allele: mutation in primer binding
Allelic drop out: failure to amplify or detect one allele in a heterozygote
Both can give an erroneous homozygote profile when the true profile is in fact a heterozygote
How do you avoid null alleles or allelic drop out?
Null alleles: remove markers with null alleles when validating the test
Allelic drop out: use sufficient template DNA for PCR and mitigated by using duplicate PCRs
OR use a stat solution by using p or 2p to calculate the probability of a homozygote genotype instead of p^2
Do you want a HIGH or LOW RMP? What does RMP stand for?
RMP: random match probability
Want it to be LOW, because this means that there is a low probability that another random individual will be identical at the loci tested
How is population assignment used in wildlife forensicfs?
Population assignment tests can be used to determine the population of origin of the sample in question.
Use same microsatellite DNA markers as in DNA matching
Compares the likelihood of a DNA profile originating from one location versus another
Likelihood is given by the frequency in which alleles in a DNA profile can be found in different populations
When are population assignment tests possible?
Only possible if there is sufficient genetic differentiation between subpopulations.
Ideally populations are geographically discrete
