Forensic Biology Flashcards
subcategories of forensic biology
- serology
- DNA testing
serology
screening of evidence for body fluids
DNA testing
efforts to individualize the body fluid to a specific person
sources of DNA evidence
- blood
- semen
- saliva
- urine
- hair
- teeth
- bone
- any soft tissue
what source of DNA is lowest in DNA?
urine
what part of blood does not have DNA?
RBC
mitochondrial DNA
comes from the mother
nucleus DNA
comes from both parents
______ base pairs of mitochondrial DNA encode for only _____ genes
16,569 , 37
_________ base pairs, _______ are exactly the same
3 billion , 99.9%
how many chromosomes? how many pairs?
- 46 chromosomes
- 23 pairs
what does A pair with?
T
what does C pair with?
G
what pair together?
pyrimidines and purines
for each chromosome pair, how many comes from each parent?
one
locus
specific, physical location of a DNA sequence on a chromosome
human identity testing
- forensic cases
- convicted felon DNA databases
- missing persons cases
- paternity tests
- mass disasters
- military DNA “dog tag”
human identity testing: forensic cases
matching or excluding a suspect with evidence
human identity testing: missing persons cases
identifying the remains
human identity testing: paternity tests
identifying the father
human identity testing: mass disasters
putting familial pieces back together
what do you compare in human identity testing?
questions sample and known samples
questioned samples
whatever is at the scene
known samples
a sample taken from a suspect
ABO blood typing
first genetic evidence used in court
ABO blood typing details
- after 1915 increasingly used in forensics/ paternity
- great for exclusion, poor for inclusion
Karl Landsteiner
discovered blood types
discriminating power
- the probability of discriminating two distinct samples selected at random from the population of interest
- can vary in populations
random match probability
probability of matching someone else by random chance
what are ABO Blood Antigens made of?
sugar on the outside of blood cells
forensic protein profiling: normal gene
normal protein
forensic protein profiling: mutated gene
- abnormal protein
- no protein
- functional protein variant isoenzyme
Functional Protein Variant Isoenzyme
enzymes that differ in amino acid sequence but catalyze the same chemical reaction
forensic protein profiling
- power of discrimination can be one in several hundred if using multiple
- proteins are not as variable & stable as DNA
pI
the pH at which the protein is electrically neutral
steps of forensic protein profiling
- an ampholyte solution is incorporated into a gel
- stable pH gradient is established in the gel after application of electric field
- protein solution is added & electric field is reapplied
- after staining, proteins are shown to be distributed along pH gradient according to their pI values
advantages of forensic protein profiling
improved power of discrimination over blood group typing
limitations of forensic protein profiling
- poor power of discrimination even with multiple systems
- poor sensitivity
- proteins are not always stable in forensic stains or found in every single sample
first decade of forensic DNA typing: 1980
- Restriction Fragment Length Polymorphism
- multiallelic
- passed down through multiple generations
multiallelic
there is a locus with a lot of variability
first decade of forensic DNA typing: 1985
- RFLP techniques used in a forensic case
- previously used in paternity & immigration
- 1st scientifically accepted forensic DNA analysis method in the USA
- now replaced with newer techniques
the principals of RFLP testing
- cut the DNA with biological scissors (restriction enzymes)
- separate fragments of differing length by gel electrophoresis
- detect length-based differences (polymorphisms) in DNA fragments of interest
restriction digest
cutting DNA into small, variably sized, pieces with restriction enzymes called restriction endonucleases
restriction enzyme
bacterial protein that cuts foreign DNA
what does variability in tandem repeats create?
different sizes
separating DNA fragments after a restriction digest with gel electrophoresis
- an agarose gel is porous allowing movement of DNA fragments
- opposites attract
- DNA has an overall negative charge
- larger DNA fragments quickly get stuck in the porous gel
- shorter fragments travel a longer distance toward the anode
VNTR’s - Variable Number Tandem Repeats
only DNA fragments containing a complementary sequence to the probe are detected
southern blot
- double stranded fragments
- single stranded fragments
- visualize with probe
DNA finger printing
matching bands from blood sample to people
multi-locus probe
complex patterns
single-locus probe
better for forensic samples containing mixtures
DNA evidence and Monica Lewinsky’s Blue Dress
- 1998 FBI report on analysis of the stain on Monica Lewinsky’s blue dress
- lied about infidelity & could have been impeached
