EXAM 3: ch.10/11 DNA degradation and LCN Flashcards
Discuss advantages and disadvantages of
miniSTR assays.
CHECK
adv. - (moving PCR primers)- you can identify degraded DNA,
dis.- you can only test for 8 loci
Name at least two ways that the presence of a
mixture can be detected.
- stutter appears abnormally high
*severe peak height imbalance
What are the causes of allele drop-in and allele
drop-out in the context of amplifying low
amounts of DNA template?
CHECK
LCN ; allele drop in means you have such small quantities you have small limits so low DNA is amplified
not enough , so one allele may not be amplified
how does DNA degradation happen?
water,oxygen, nucleases, UV radiation
who uses degraded DNA
miniSTR/ SNPs
what significant event used miniSTR
WTC identification
disadvantages of miniSTR
few loci can be multiplexed
decay curve is seen …
degraded DNA
DNA degradation means less
Loci work (lower peak heights & loss of alleles)
true or false: with degraded DNA samples information is simply lost at the larger sized STR loci
true
DNA profiles are essentially a pair of numbers..
if DNA was damaged then the string of numbers is shorter and less informative
Low copy number (LCN) comes from..
low profile touch DNA samples
where can you get touch DNA from
fingerprint residues or secondary transfer (skin cells)
what are some precautions for using LCN
- at least 2 amplifications from the same DNA extract
-sterile environment
-elimination database
what are some issues with LCN?
- allele dropout
- stutter peaks enhanced
-peak height imbalance
-sporadic contamination
3 ways to indicate if something is a mixture :
- do any of the loci show more than 2 peaks
- is there a severe peak height imbalance
- does the stutter product appear abnormally high
how do mixtures arise ?
when two or more individuals contribute to the sample being tested
when can mixtures be hard to detect ?
degraded DNA
what process (learned previously) can help distinguish male and female components
differential extraction (with the help of Y chromosome markers)
6 steps in interpreting a mixture
- Identify presence of mixture
- Designate allele peaks
- Identify number of potential contributors
- Estimate relative ratio of individuals in mixture
- Consider all possible genotype combinations
- Compare reference samples
