Forensic Science: An Introduction

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 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. From the victim 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 Rape Evidence

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 • 1 1x107 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