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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) – antigen-antibody test for p30 protein found in semen; very sensitive
Rape EvidenceFrom 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
DNA
• DeoxyriboNucleic 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 and proof-
reads 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 1x107 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
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