FORENSICS: DNA Test Review
what is mitochondrial DNA?
DNA found in the mitochondria (energy producing structures), not in the nucleus
which process uses enzymes?
PCR
what is DNA composed of?
nucleotides
what is VNTR used for?
to match parents
what does VNTR stand for?
variable number of tandem repeats
what are Y-STR's helpful?
-
what is mDNA?
- DNA inherited from the mother - the same for siblings and the mother - not useable to individualize a person, but useful to establish family relations
T/F: all DNA evidence will result in a usable profile.
F
what are Y-STR's?
STR's associated with the Y chromosome
what are the 3 types of DNA analysis?
STR, VNTR, RFLP
what's the most common type of DNA analysis? why?
STR, it takes less time and less samples
whats the difference between STR, PCR, VNTR, RFLP?
STR- specific loci PCR- short sequence that starts replication VNTR- cuts after very long sequences RFLP- found on chromosomes that match fathers
T/F: the DNA in a man's heart is the same as the DNA in his skin cells and saliva.
T
how can DNA evidence be contaminated?
VERY EASILY... by touching or sneezing
who discovered DNA and when?
Watson and Crick (made diagram) with the help of Rosalind Franklin (x-rays), 1950
what are the four bases?
adenine, thymine, guanine, cytosine (A pairs with T, G pairs with C)
what are alternative forms of a gene called?
alleles
why is RFLP not used anymore?
because the entire DNA molecule is too complicated to analyze
where is DNA evidence found?
blood, semen, and skin cells (saliva, sweat, mucus, skin, ear wax, vaginal secretions)
what does DNA make up?
chromosomes of the human body
what is the shape of mitochondrial DNA?
circular
what does CODIS stand for?
combined DNA index system
what does PCR do?
copies a fragment of DNA to get a big enough fragment to see it
what do restriction enzymes do?
cut DNA at specific sequences
what does DNA stand for?
deoxyribonucleic acid
what is the structure of DNA?
double helix
what is DNA fingerprinting?
gel electrophoresis
what are objects that DNA can be retrieved from?
gum, stamps, envelopes, washed stains (blood, semen), door knobs, tooth brushes, sanitary pads, tooth pulp, sweaty clothes, phones, bone marrow, hair brushes
what do VNTR's do?
identify repeats of 9-80 base pairs
when will VNTR's appear as the same band?
if they are close to the same number
what is the loci?
location of a gene (STR)
what are short tandem repeats?
locations on a chromosome that repeats a specific sequence of 2-5 base pairs
what does PCR stand for?
polymerase chain rxn
what controls do the forensic department use to prevent contamination?
protective gloves, mask, hairnet
what does RFLP stand for?
restriction fragment length polymorphism
what does STR stand for?
short tandem repeats
what might a child leave behind the would contain their DNA?
skin cells, saliva
what is PCR used for?
small pieces of DNA to replicate multiple copies using DNA polymerase (the replication process)
what's a nucleotide made of?
sugar, phosphate, base
what can affect DNA evidence at a crime scene?
sunlight, humidity, heat
who maintains CODIS?
the FBI (local, state, and national)
what is the total probability of finding the combination of DNA?
the product of the individual probabilities
what does a DNA ladder show? what does it give you?
the size of fragments && gives a known sample size
what happens when bands are the same size?
they are darker
what are probes?
they make DNA appear by highlighting the OPPOSITE
are VNTR's inherited?
yes
do you have to use the same restriction enzyme to compare?
yes
do a baby's bands match their parents'?
yes, they match mom, dad, or both
what are the 5 steps of electrophoresis?
1. DNA is CUT with restriction enzyme 2. it is placed in AGAROSE GEL WELL 3. electric CURRENT is passed through gel 4. it is ATTRACTED to a positive electrode (due to DNA's negative charge) 5. fragments are separated by SIZE (largest are closest to the well)
what are the 6 steps of DNA analysis?
1. collect sample 2. determine if the samples is appropriate to be analyzed 3. remove sample 4. remove other cellular components 5. using enzymes, release DNA from chromosomes 6. DNA is now ready for characterization
what are the 5 rules of DNA collection?
1. gloves 2. stained articles go in paper bags 3. refrigerated or stored in a cool, dry place 4. blood found in soil must be frozen (microbes) 5. buccal swabs to compare (need warrant, unless it's from trash)
what are the 4 steps of DNA fingerprinting?
1. isolate DNA 2. PCR 3. gel electrophoresis 4. read band pattern
how is DNA replicated? (3 steps)
1. the parent DNA unravels 2. new bases pair with each side 3. 2 new COMPLEMENTARY strands are formed
what are the 5 forensic uses of DNA?
1. to identify suspects 2. to clear a wrongly accused person 3. to identify crime 4. to establish family relationships 5. to match organ donors with recipients
what are the 3 benefits of PCR?
1. you only need a very small amount of biological material 2. it can be used with forensic samples (only a few hundred base pairs are effective) 3. contaminated DNA (fungal and bacteria) will not show up
how many STR's are looked for in DNA evidence?
13
what ends do restriction enzymes produce?
BLUNT- don't connect STICKY- able to connect with other segments
what is the database of DNA profiles of convicts help identify suspects of certain crimes (rape, murder)?
CODIS
what are the 2 sets of databases?
OFFENDERS- varies as to who is entered (all sex offenders, some states all felons, one state anyone arrested) FORENSIC FILE- DNA profiles from crime scenes
