Final exam Flashcards
Francis Bacon – Observation
Scientists should be disinterested observers
Collect observations without prejudice or preconception
Multiple observations lead to emerging patterns that can provide “truths about nature”.
Karl Popper – Falsification
Hypothesis emerges from observation
Logical predictions follow from the hypothesis
Predictions can be tested in such a way as to allow for rejection of the hypothesis.
Hypotheses can only be “rejected” or “fail to be rejected”,
they can never be proven.
Thomas Kuhn – Paradigm shift
He suggested that there is a consensual world view that involves an agreed upon set of assumptions, methods, and language (a paradigm) in which science progresses incrementally.
At a certain point there builds up difficulties and eventually a scientific revolution brings about a new paradigm.
Science (like law) is an adversarial process:
differences
where the falsification of hypotheses and construction of alternative hypotheses occurs. No feelings in science
Differnces – timing, testing of hypothesis, language
Comparison of science & the law
Language:
error and mistake. Used interchangeably in law. Error is intrinsic to any scientific measurement and is part of the data interpretation.
Objective:
Law – justice within a time limit. A decision has to be made.
Science – truth with no time limit. A decision is not required.
Individualization:
advantage and problem
assume indistinguishable marks produced by a single object and those produced by different people or objects are observably different.
Advantage/appeal: enables forensic scientists to draw bold, definitive conclusions.
PROBLEM: excuses forensic sciences from developing: measures of object attributes, collecting population data on the frequencies of variations in those attributes, testing attribute independence, and calculating and explaining probability that different objects share common observable attributes.
Innocence project evidence
Stephen Cowan - Fingerprint
Ray Crone - Bite mark
J.R. Brouingaard - Head/Pubic hair
Ronald Cotton - Eye witness
Frye Standard (1923): “general acceptance”
the general acceptance of the scientific technique or principle
Daubert:
new rules for admissibility of scientific expert testimony. Difficult for courts to sort good from bad science, whether the bad science is a matter of perjury, incompetence, or unclear language.
Expert Testimony:
peer review, error rates, adequate testing, regular standards and techniques, general acceptance.
Theoretical underpinnings of methods must yield testable predictions by means of which the theory could be falsified.
Methods preferably published in peer-reviewed journal.
Known rate of error that can be used to evaluate results.
Methods generally accepted by relevant scientific community.
Blood tests
colour tests such as Kastle-Mayer/Hemastix
luminescence tests: luminol/Bluestar
antibody precipitin tests, specific for human blood: Hematrace test.
Semen Tests
Direct microscopic observations
acid phosphatase test (colour test)
prostate specific antigen tests (P30 human specific)
Saliva
Phadebas Test (for alpha-amylase)
how is Species identification perfromed
Species identification is performed using DNA markers (mitochondrial DNA sequencing).
Sex determination
PCR amplification of X and Y chromosomespecific DNA allows sex determination. .
Individual identification
DNA analysis can identify evidence taken from an illegal kill site and “link” it to a sample from suspected poacher
Population identification
Databases needed for population identification (e.g. reference samples).
Parentage
Establish if animals in a captive breeding program are the offspring of registered breeding pairs or illegally obtained from wild stocks (again with STRs or microsatellite markers)
Tests you can’t mix together
DNA analysis + chemical testing
Serological testing + DNA analysis
Trace evidence + DNA analysis
Toxicology + DNA analysis
Parentage Biology
DNA Extraction –> DNA Quantitation –> PCR Amplification of Multiple STR markers
Parentage technology
Separation and Detection of PCR Products (STR Alleles) –> Sample Genotype Determination
Parentage genetics
Comparison of Sample Genotype to Other Sample Results –> If match occurs, comparison of DNA profile to population databases –> Generation of Case Report with Probability of Random Match
PCR
copies
used molecular biology technique that allows scientists to make millions or even billions of copies of a specific segment of DNA.
genotype
A genotype refers to the genetic makeup of an organism, which is the collection of genes inherited from its parent
random probability match
the significance of a DNA match and its potential occurrence in the broader population
Ex. Not many people have red hair so if red is found you can look at the general population and realize that there arent many gingers so it has to be the suspect
human vs wildlife forensics
Same principles as human forensics.
Main difference: need to identify and distinguish between a variety of species. not for humans
Differential extraction
The purpose of differential extraction is to isolate DNA from different cell types (for example, sperm cells and epithelial cells from the victim) based on their different physical and chemical properties
What would a profile look like for STR for males
3 peaks then there is less than 2 people involved
Each marker represents a specific region on the Y chromosome where the number of repeated DNA sequences (repeats) varies among individuals.
parentage in humans on chart
baby inherits #’s from mom or dad
National DNA Data Bank: two principal programs
Convicted Offender Index (COI) : electronic index developed from DNA profiles collected from offenders convicted of designated primary and secondary offences.
The Crime Scene Index (CSI) : separate electronic index composed of DNA profiles obtained from crime scene investigations.
Missing person index