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Forensic Science: An Introduction

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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

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