1. Forensic Science: An Introduction
Blood and DNA

2. Blood Components Formed Elements (cells) – 45%
Erythrocytes - Red Blood Cells
carry oxygen
Leukocytes – White Blood Cells
fight infections; have nuclear DNA
Thrombocytes – platelets for clotting
Plasma – 55%; Fluid portion of unclotted blood
Serum – liquid that separates from blood when clotted

3. Antigens & Antibodies Antigens - proteins found on surface of RBCs
Antibodies - proteins found in serum
Destroys or inactivates a specific antigen
Binds to two different antigens at a time and causes agglutination (clumping)
Serology – the study of
antigen-antibody reactions

4. Blood Type Blood type Antigens Antibodies A Anti-B B Anti-A AB
Both A & B
Neither Anti-A or Anti-B O
Neither A or B
Both Anti-A or Anti-B
Rh factor – have it (+) or not (-)

5. Immunoassay
Animals can be exposed to drug-protein complexes to produce antibodies against the drug. The antibodies can then be used to as a presumptive test for drugs
Enzyme-multiplied immunoassay technique (EMIT) – labels antibody with enzyme that can cause a color change
Radioimmunoassays- antibodies labeled with radioactive tag

6. Making Antibodies
Polyclonal antibodies – produced by injecting animals with a specific antigen, A series of antibodies are produced responding to a variety of different sites on the antigen.

7. Monoclonal Antibodies
A collection of identical antibodies that interact with a single antigen site
Hybridoma – fused
plasma cell (from
spleen) and tumor
cells to produce a
limitless supply of I
dentical monoclonal
antibodies

8. Forensic Characterization of Blood Stains
Kastle-Myer – tests for hemoglobin to presume that sample is blood
Luminol – binds with blood and emits light; very sensitive
Microcrystalline tests- chemicals added to blood cause crystals to form; less specific
Precipitin test – antihuman antibodies react with human blood to identify as such
Gel Diffusion – antigens and antibodies placed in holes in an agar plate. If they react they leave a line of precipitation that is visible.

9. Blood Stain Patterns
Surface texture is important; the harder and less porous, the less splatter
The direction of travel of the blood can be determined by its shape
The angle of the impact can be determined by the circular distortion of the drop.
The origin of blood splatter can be determined by converging the long axes of several drops to create a 2 D origin

10. Heredity Zygote Sperm/egg Chromosome Gene Allele Locus DNA Homozygous
Heterozygous
Genotype
Phenotype

11. Paternity testing
Used to identify is a male is the father of a specific child
ABO system
HLA antigens – 90%
DNA – 99% +

12. Semen Acid phosphatase – enzyme found in high concentration is semen
Can be visualize when reacted with certain chemicals and exposed to UV light
Microscopy – located spermatozoa
Prostate Specific Antigen (PSA) – antigen-antibody test for p30 protein found in semen; very sensitive

13. Rape Evidence From the victim From the suspect Pubic combings
Pubic hair standard/reference sample
External genital dry-skin areas
Vaginal swabs and smears
Cervix swabs
Rectal swabs and smears (
Oral swabs and smears
Head hairs
Blood sample
Fingernail scrapings
All clothing
Urine specimen
From the suspect
All clothing
Pubic hair combings
Pulled head and pubic hair standard/reference samples
Penile swab
Blood or buccal swab

14. DNA DeoxyriboNucleic Acid Found in the nucleus 46 chromosomes
25,000 genes
Structure determined by Crick and Watson
DNA fingerprinting by Alec Jeffreys

15. Structure of DNA A polymer made of repeating nucleotides
Nucleotide consists of a deoxyribose sugar, a phosphate, and a nitrogen base (Adenine, Thymine, Cytosine, or Guanine)
Double stranded, helical
Complementary base
pairing, A=T, G=C

16. DNA at Work
DNA in nucleus is copied into a strand of RNA (transcription)
RNA is read at the ribosome to make assemble amino acids into proteins (translation)
Every 3 bases on DNA
codes for a different
amino acid

17. Replication of DNA
Replication – the synthesis of new DNA from existing DNA in the nucleus
DNA polymerase assembles
new DNA strand and proof-
reads it
Replication occurs in nucleus prior to cell division

18. Polymerase Chain Reaction
A technique for replication, or amplifying, a portion of DNA outside
the cell
Each cycle doubles
the number of copies
x107 in 30 cycles

19. DNA Typing with Tandem Repeats
Region of chromosome that contains multiple copies of a core DNA sequence arranging in a repeating fashion between the coding regions (genes)
Restriction Fragment Length Polymorphisms used enzymes to cut the DNA around these tandem repeat sites and then run them on a gel electrophoresis
A Southern blot was then performed and radioactive probes were hybridized to help visualize the RFLPs

20. RFLPs

21. PCR PCR has the following advantages: 1. PCR can use shorter sequences
2. shorter pieces more stable
3. smaller amounts of DNA can
be used (10-9 gram)

22. Short Tandem Repeats (STRs)
A region of a DNA molecule that contains short segments of 3-7 repeating base pairs.
Generally less than 450 bp long
Less degradation
Can be PCR’d
Can multiplex a large number of these STRs at once
US uses 13 STRs for tests

23. Capillary electrophoresis
Sex Identification by focusing on the
amelogenin gene

24. Mitochondrial DNA
Cell organelle responsible for supplying energy to the cell by producing ATP from glucose
Mitochondria has its own DNA
Inherited solely from mother
Used for identification when nuclear DNA is degraded
Reference sample can be maternal relative

25. CODIS
A computer software program developed by the FBI that contains local, state and national databases of DNA profiles from convicted offenders, unsolved crime-scene evidence, and profiles of missing people

26. Collection and Preservation
Can use low copy samples
Avoid contamination; change gloves before each new sample
Collect substrate controls/reference samples (buccal swabs)
Package in air tight containers