DNA Criminalist and Court Appearance Margaret Aceves State of California Dept. Of Justice Jan...
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Transcript of DNA Criminalist and Court Appearance Margaret Aceves State of California Dept. Of Justice Jan...
Margaret AcevesState of CaliforniaDept. Of Justice
Jan Bashinski DNA Laboratory
If Case goes to Court, Our role as Criminalists is to present the facts to the
jury
Case approach is to leave sufficient evidence for re-analysis.
DNA Criminalist in courtDeputy District Attorney qualifies DNA Analyst as
an expert through their education, training and experience
What is DNA is explained to the court and jury.The DNA Analysis is briefly explainedSpecific DNA results are presented Significances of match is explained
Education of a DNA Analyst A Bachelors degree in a Natural Science
AND
FBI requires specific courses to participate in CODIS Molecular Biology Genetics Biochemistry Training in statistics
Qualifying as an Expert
•Training of a DNA Analyst
•Experience of a DNA Analyst
•How many cases completed•How many times have you testified•Results of Proficiency
DNA BasicsWhat is DNA?
DNA stands for Deoxyribonucleic Acid
• It is the genetic material found in all plants and animals.• “Blueprint of Life” – It contains all of the information for
passing genetic traits from one generation to the next generation.
Where is DNA found in your body?
Our bodies are made up of cells.
The nucleus of each cell contains DNA.
Types of Biological EvidenceBloodBloodSemenSemenSalivaSalivaHairHairSweatSweatTeethTeethBoneBoneTissueTissueUrineUrine
Important Point: All cells in your body have the same DNA.
How is DNA inherited?
½ is inherited from your Mother½ is inherited from your Father
DNA is packaged in the form of chromosomes.
Humans have 23 pairs of chromosomes.
Terms to Understand
Chromosome – Physical structure that DNA is packaged in. Humans have 23 pairs.
Genetic Marker (locus) – specific location on a chromosome.
Allele – Alternative possibility for a genetic marker.
Forensic DNA TypingMore than 99% of our DNA is the same (this is why we all
have one head, two eyes, two arms, two legs, etc).Short tandem repeats (STRs) are used in forensic DNA
typing.STRs vary from person to person by the number of the
repeating sequences.
the repeat region is variable between samples while the flanking regions are constant
7 repeats
8 repeats
AATG
CSF1PO
D5S818
D21S11
TH01
TPOX
D13S317
D7S820
D16S539 D18S51
D8S1179
D3S1358
FGA
VWA
Location of13 CODIS Core STR Loci
AMEL
AMEL
Sex-typing
Process of Forensic DNA AnalysisDocument evidenceSample evidenceApply chemicals and
heat to separate the DNA from the rest of the cellular components
Purify DNADetermine
concentration of DNA
Actual AnalysisHours of on hands
sample manipulation
How much DNA?qPCR Instrument to
quantitate the DNA extract
Amplification of DNAPolymerase Chain
Reaction (PCR)Areas of DNA are
replicated millions of times.
Applied Biosystems 3130 Genetic Analyzer
DNA Analysis-hours at the computer!
Identifiler- 15 loci and amelogenin
Identifiler- 15 loci and amelogenin
Identifiler Tables
IDENTIFILER LOCI
Analysis continuedA report with a table of results is generatedThe laboratory work and report are technically reviewed
by a qualified analyst.The laboratory work and report are administratively
reviewed.Report is released.
Comparison of Genetic Profiles
Possible Outcomes of comparison of DNA Results to
Known Reference DNA profiles
•Inclusion (reference profile matches evidence profile)
•Exclusion (reference profile does not match evidence profile)
•Inconclusive (not enough information to make comparison)
Matching results from comparisonWhat is the significance of a match between the
reference profile and the evidence profile? Another way to think about this question is: How rare is the evidence profile in the population?
How rare is the evidence profile?First: Population StudyA study that counts how many times a certain allele is seen
for a genetic maker.The published data from the FBI is used for the 3 major
racial/ethnic groups (Caucasian, African American and Hispanic).
STR Allele Frequencies
0
5
10
15
20
25
30
35
40
45
6 7 8 9 9.3 10
Caucasians (N=427)
Blacks (N=414)
Hispanics (N=414)
TH01 Marker
*Proc. Int. Sym. Hum. ID (Promega) 1997, p. 34
Number of repeats
Per
cen
t
Conveying Frequency•A dice is six-sided. Therefore one in six= 1/6=0.1667.
•A 20-car parking lot full of cars, how many are blue? 5, 5 in 20= 5/20= 0.25
How rare is the evidence profile?Second: Apply StatistiMultiply the allele frequencies for each genetic marker.
Evidence
D3S1358
15 , 16
.24631 or 25% .23153 or 23%
(in Caucasians)
X = .11
How rare is the evidence profile?Second: Apply StatisticsMultiply the frequencies for each genetic marker together
to determine the overall frequency for entire the profile.
VWAD3S1358 FGA
.11
15, 16
D8S1179
16, 18 22,25 13, 15
.09 .03 .07X X X
Frequencies of 11 more genetic markers =
1 in # quadrillion,
15 zeros
Discrimination power of Identifiler
Population of Calif. and USA
World Population ~ 6.79 Billion
ConclusionThe evidence is presented and the strength of the match
conveyed.
We leave the decision of guilt or innocence for the jury to decide.