Forensic Science An Introduction Blood and DNA Blood

Forensic Science: An Introduction Blood and DNA

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

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

Blood Type Blood type Antigens Antibodies A A Anti-B 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 (-)

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

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.

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

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.

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

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

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

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) – antigenantibody test for p 30 protein found in semen; very sensitive

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 • All clothing • Pubic hair combings • Pulled head and pubic hair standard/reference samples • Penile swab • Blood or buccal swab

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

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

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

Replication of DNA • Replication – the synthesis of new DNA from existing DNA in the nucleus • DNA polymerase assembles new DNA strand proofreads it • Replication occurs in nucleus prior to cell division

Polymerase Chain Reaction • A technique for replication, or amplifying, a portion of DNA outside the cell • Each cycle doubles the number of copies • 1 1 x 107 in 30 cycles

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

RFLPs

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)

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

• Capillary electrophoresis • Sex Identification by focusing on the amelogenin gene

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

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

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