lec 11 - dna forensics Flashcards
1
Q
forensic science
A
intersection btw law and science
2
Q
evolution of dna fingerprinting
A
- 1800s photography (but can change appearance)
- 1900s fingerprints (but can be smudged)
- 1985 DNA fingerprinting (unique genetic signature)
3
Q
why is DNA fingerprinting superior?
A
- uniform nature (every cell in body has same genetic material)
- variability btw individuals (0.1% difference generates unique DNA profile)
4
Q
restriction fragment length polymorphism (RFLP)
A
- extract DNA –> digest with restriction enzymes –> use probes to look for fragments –> run on gel to see unique bands
- exploits variations in homologous DNA sequences (polymorphisms) to pinpoint location of genes within a sequence
5
Q
list (2)
RFLP drawbacks
A
- requires large amounts of DNA
- degraded DNA cannot be used
6
Q
why is PCR better than RFLP?
A
- amplifies specific fragments of DNA
- much less DNA needed
- DNA can be partially degraded
7
Q
PCR drawback
A
extremely sensitive to contamination (even a little bit will be amplified)
8
Q
variable number tandem repeats (VNTRs)
A
- each person has different number of repeats for each loci
- inherit one locus from mother, one from father
9
Q
VNTRs
minisatellites
A
repeated sequences btw 10-100bp –> RFLP
10
Q
how to design a primer for minisatellites
A
design primer based on repeat fragments flanking minisatellite sequence (forward primer)
11
Q
VNTRs
short tandem repeats (STRs)
A
2-6 nucleotides –> PCR
12
Q
how many STRs does FBI analyze
A
- 13 unique STRs for analysis and comparison to library of DNA fingerprints
- combined DNA index system (CODIS) added 7 more
- total 20
13
Q
STR analysis
A
- uniqueness of individual’s VNTRs and STRs provides scientific marker of identity
- number of repeats within STR referred to as allele –> ex: STR on chromosome 7 contains 5-16 GATA repeats
14
Q
for 13 STR regions, odds that 2 ppl have same 13-loci DNA profile are…
A
less than 1 in a billion
15
Q
list (5)
rules for specimen collection at crime scene
A
- any source of DNA can be source of contamination
- disposable gloves and instruments
- avoid talking, sneezing, coughing
- avoid touching areas that might contain DNA (face, nose, mouth)
- air dry evidence before packaging
- store evidence in specifically designed materials
16
Q
list (3)
enemies of evidence
A
- sunlight and high temperatures
- bacteria (decomposition)
- moisture (mold)
17
Q
fingerprinting is a ____ process
A
comparative process –> samples from crime scene compared to suspect DNA
18
Q
best sample come from…
A
fresh, whole blood (luekocytes)
19
Q
can decades old sample be analyzed?
A
yes, just need PCR
20
Q
3 steps
preparing DNA fingerprint
A
- extraction of DNA: chemically (detergent) or mechanically (pressure to force DNA out)
- PCR: DNA primers complementary to flanking regions of CODIS sites –> amplification at specific STR sites
- STR analysis: alleles separated and detected using capillary electrophoresis –> bands to determine number of repeats
21
Q
first reported use of genetic fingerprinting in criminal case
A
- narborough village murders
- suspect’s DNA didn’t match those found at crime scene –> 5500 cheek swabs
- friend gave his DNA instead of suspect’s
22
Q
forest hills rapist
A
- 3 assaulted woman reported black man but suspect wasn’t black
- DNA matched at crime scene to black man (more important than eyewitnesses)
23
Q
M-vac
A
wet vacuum collection system –> extract DNA from partial or smudge of fingerprint –> amplify
24
Q
protein analysis instead of DNA
A
- mass spectrometry-based shotgun proteomics
- proteins more chemically robust than DNA
- contains genetic variation in single amino acid polymorphism (SAPs)
25
hair analysis
- previously needed DNA from skin still attached to hair follicles
- recent tech analyzes proteins in hair itself (keratin)
26
improved hair analysis
- better extraction methods --> heat hair in detergent solution --> mass spec --> analyze genetically variant peptides (GVPs)
27
# list (3)
hair analysis drawbacks
- time consuming
- requires expertise
- sophisticated techniques
28
# list (3)
ancient DNA extraction advantages
- tracks evolutionary history of human populations
- extraction of more DNA from less material
- hair withstands centuries of heat and rain
29
forensic genealogy
taking DNA info from public databases to solve cases
30
golden state killer
identified his relatives by cross refering with public DNA databases --> constructed large family tree --> tracked him down
31
forensic genealogy ethical implication
privacy --> ppl in those databases never gave consent for their info to be used like this
32
# list (3)
chain of DNA evidence
- DNA can become tainted and not effective (OJ simpson)
- evidence collection must be systematically recorded
- access to evidence must be controlled
- follow standards of lab practice and procedures to prevent DNA damange during analysis
33
# list (2)
DNA evidence must...
- make sense to jury
- statistics must be understandable (musn't rely on outliers)
34
paternity tests
analyze samples from child and adults involved
35
mitochondrial DNA analysis
- used for samples that cannot be analyze by RFLP or STR --> older samples that lack nucleated cellular material
- inherited from mother only
- changed only 2-4% every million years due to random mutations
36
tracing maternal line
- relationships traced this way
- all children will inherit mtDNA but only daughters will transmit to next generation
37
y-chromosome analysis
passed directly from father to son
38
9/11 world trade center
- DNA techniques to identify remains of victims --> tissue samples from 3000 ppl
- horrible conditions for DNA (debris, heat, microbes)
39
new strategies for 9/11
- to quickly prepare and organize DNA profiles --> compare to relatives DNA
- within 24 hours, collected samples from persons and families
40
new software program for 9/11
matched DNA samples from family to those of victims using STR, mtDNA, and SNP analysis
41
south asian tsunami
modified 9/11 software to include y-chromosome analysis
42
# food applications
ginseng
- one native to north america (calmness), one to asia (energy)
- cannot be differentiated just by looking --> must look at DNA level
- american variety rare and more valuable
43
# food applications
cabernet sauvignon grapes
- DNA evidence determined ancestors of thse grapes are cabernet franc and sauvignon blanc
- hybrid grape inferior and legally excluded in france
44
DNA tagging
- as authentication labels hidden in products --> prevents counterfeiting
- superbowl footballs, olympic merch, food fraud (mislabelling and GMO testing)
