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