fs ch 14
TRANSCRIPT
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Chapter 14
Biological Stain Analysis: DNA
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Forensic ScienceRichard Saferstein
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Nature of Blood Blood:-cells/enzymes/proteins/inorganic
substances Plasma:-fluid portion/water Red blood cells (erythrocytes) White blood cells (leukocytes) Platelets Antigens:-proteins-surface of red blood cells/blood-type
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Forensic ScienceRichard Saferstein
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Blood Typing A-B-O and Rh systems Type A Type B Type AB Type O Rh factor:
-D antigen.
-Rh positive
-Rh negative. agglutination
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Forensic ScienceRichard Saferstein
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Forensics of Blood1. Blood?
2. Species
3.Human-particular individual?
Preliminary color test.
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Forensic ScienceRichard Saferstein
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Blood Tests Kastle-Meyer-color test-deep pink Luminol:-luminescent-old blood Microcrystalline tests:-Takayama -Teichmann
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Forensic ScienceRichard Saferstein
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Blood Origin Testing Blood? Yes
Origin?
-precipitin test
-antisera
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Forensic ScienceRichard Saferstein
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Individualizing Bloodstains Human? Yes:
-particular individual
-Deoxyribonucleic Acid (DNA)
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Forensic ScienceRichard Saferstein
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Testing for Seminal Stains Sex offenses:
-seminal stains-acid phosphatase color test-purple color = acid phosphatase enzyme-spermatozoa-p30-DNA typing
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Forensic ScienceRichard Saferstein
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Sexual Assault Evidence Victim
-medical examination-ASAP -clothing/hairs/vaginal and rectal-clothing removed/packaged separately -bedding/object
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Forensic ScienceRichard Saferstein
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SEXUAL ASSAULT EVIDENCE Suspect:-24 hours-victim’s DNA -penile swab-clothing/pubic hair/head hair/penile swab-blood sample/buccal swab-physical contact between victim and
assailant-transfer:-blood/semen/saliva/hairs/fibers
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Forensic ScienceRichard Saferstein
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Introduction DNA structure:-unique as fingerprints
Gene:-unit of heredity. -composed of DNA-positioned on chromosomes-threadlike bodies-nucleus of cell
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Forensic ScienceRichard Saferstein
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Sex Determination X chromosome-mom Y chromosome-dad
-XX=female-YY=male
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Forensic ScienceRichard Saferstein
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Alleles Locus:-gene position Alleles:-alternate form of genes Homozygous:-2 similar alleles Heterozygous:-2 different alleles
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Forensic ScienceRichard Saferstein
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The Structure of DNA DNA:-large molecule/-nucleotides-sugar/phosphorous-containing group/nitrogen-
containing molecule called a base Four types:-adenine (A)-guanine (G)-cytosine (C) -thymine (T). double-helix configuration Base pairing-A w/TG w/ C
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Forensic ScienceRichard Saferstein
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DNA Replication Prior to cell division/unwinding of double helix Strands exposed to collection of nucleotides:-recreate the double helix-letter by letter-base pairing
Polymerase chain reaction (PCR):-replicates small quantities-sample size no longer limiting
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Forensic ScienceRichard Saferstein
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PCR Testing Advantage-amplify minute quantities-millions of times
Heated to separation Primers:-target specific regions-hybridize with the strands DNA polymerase/free nucleotides added:-rebuild each strands.-process repeated 25 to 30 times
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Forensic ScienceRichard Saferstein
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DNA Typing DNA molecule
-sequences of bases repeated numerous times (tandem repeats)
-means of distinguishing one individual from another DNA typing.
-filler/spacers between coding regions of DNA
-all humans have same type of repeats-tremendous variation in number of repeats indivually
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Forensic ScienceRichard Saferstein
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Short Tandem Repeats (STRs) STR analysis;-most successful/widely used DNA profiling
procedure-STRs: locations on chromosome that contain
short sequences that repeat themselves within the DNA molecule
-useful markers for identification -great abundance throughout the human
genome
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Forensic ScienceRichard Saferstein
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STR Advantages STRs:
-repeating sequences of 3-7 bases in length-entire strand very short-less susceptible to degradation-recovered from bodies/stains subjected to
decomposition-ideal candidates for multiplication by PCR-overcoming limited sample size associated
with crime-scene evidence
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Forensic ScienceRichard Saferstein
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The Power of STR Hundreds of different types of STRs are
found in human genes:
-more STRs characterized-smaller the percentage of the population a particular combination of STRs came from
-multiplexing-simultaneously extract/amplify combination
of different STRs
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Forensic ScienceRichard Saferstein
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Standardizing STR Testing U.S. crime laboratories-standardized on 13
STRs for entry into CODIS
-high degree of discrimination/individualization attained by multiplexing/determining product of their frequencies
-125 picograms of DNA for analysis
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Forensic ScienceRichard Saferstein
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Capillary Electrophoresis Capillary electrophoresis:- separates DNA fragments on a thin glass
column-end immersed in reservoir of buffer liquid
w/ electrodes-sample solution is injected into one end of
column-STR fragments move through the electrified
column at a speed that is related to the length of the STR fragments
-DNA peaks pass through the detector (electropherogram)
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Forensic ScienceRichard Saferstein
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Sex Determination by STRs Amelogenin gene:
-tooth pulp-shorter by six bases in the X
chromosome-amelogenin gene amplified by
PCR/separated by electrophoresis-males-two bands-females-one band
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Forensic ScienceRichard Saferstein
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Mitochondrial DNA Located outside nucleus:
-mother-structures found in all energy cells-single mitochondria contains
several loops of DNA
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Forensic ScienceRichard Saferstein
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Mitochondrial DNA Testing Reserved for samples (hair) when STR not
possible-analysis more rigorous-time consuming-costly -compared to nuclear DNA analysis-same maternal lineage will be indistinguishable
Two regions highly variable-sequencing-determines the order of base pairs
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Forensic ScienceRichard Saferstein
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CODIS DNA typing:-compare DNA types from crime scene
convicted sex offenders/felons CODIS (Combined DNA Index System):-computer software program -maintains DNA profiles from convicted
offenders/ unsolved crimes/profiles of missing persons
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Forensic ScienceRichard Saferstein
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Packaging Biological Evidence Photograph/sketches
Latex gloves
Clothing from victim/suspect with blood evidence must be collected
Paper versus plastic
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Forensic ScienceRichard Saferstein
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Packaging Biological Evidence
Package separately in a paper bag/well-ventilated box
Dried blood:
-sterile cotton swab w/distilled water
-air dry
-swab box
-paper/manila envelope
-refrigerated
-Standard/reference specimens collected