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Chapter 14 Biological Stain Analysis: DNA

Fs Ch 14

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  • 1.Chapter 14 Biological Stain Analysis: DNA

2. 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

3. 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

4. Forensics of Blood

    • Blood?
    • Species
    • 3.Human-particular individual?
  • Preliminary color test.

5. Blood Tests

  • Kastle-Meyer
  • -color test
  • -deep pink
  • Luminol:
  • -luminescent
  • -old blood
  • Microcrystalline tests:
  • -T akayama
  • - Teichmann

6. Blood Origin Testing

  • Blood? Yes
  • Origin?
  • -precipitin test
  • -antisera

7. Individualizing Bloodstains

  • Human? Yes:
  • -particular individual
  • -Deoxyribonucleic Acid (DNA)

8. Testing for Seminal Stains

  • Sex offenses:
  • -seminal stains
  • -acid phosphatase color test
  • -purple color = acid phosphatase enzyme
  • -spermatozoa
  • -p30
  • -DNA typing

9. Sexual Assault Evidence

  • Victim
  • -medical examination
  • -ASAP
  • -clothing/hairs/vaginal and rectal
  • -clothing removed/packaged separately
  • -bedding/object

10. SEXUAL ASSAULT EVIDENCE

  • Suspect:
  • -24 hours
  • -victims 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

11. Introduction

  • DNA structure:
  • -unique as fingerprints
  • Gene:
  • -unit of heredity.
  • -composed of DNA
  • -positioned on chromosomes
  • -threadlike bodies-nucleus of cell

12. Sex Determination

  • X chromosome-mom
  • Y chromosome-dad
  • -XX=female
  • -YY=male

13. Alleles

  • Locus:
  • -gene position
  • Alleles:
  • -alternate form of genes
  • Homozygous:
  • -2 similar alleles
  • Heterozygous:
  • -2 different alleles

14. 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/T
  • G w/ C

15. 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

16. 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

17. 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

18. 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

19. STR Advantages

  • STRs:
  • -repeating sequences of 3-7 bases in length
  • -entire strand very short
  • -less susceptible to degradation
  • -recovered from bodies/stains subjected todecomposition
  • -ideal candidates for multiplication by PCR
  • -overcoming limited sample size associated with crime-scene evidence

20. 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

21. 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

22. 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 (e lectropherogram)

23. 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

24. Mitochondrial DNA

  • Located outside nucleus:
  • -mother
  • -structures found in all energy cells
  • -single mitochondria contains several loops of DNA

25. 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

26. 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

27. Packaging Biological Evidence

  • Photograph/sketches
  • Latex gloves
  • Clothing from victim/suspect with blood evidence must be collected
  • Paper versus plastic

28. 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