DNA Flashcards
What is DNA?
Double helix
Nucleotides (ACTG)
Connected to a sugar molecule and phosphate group (AT and CG bonding)
Watson and Crick are given credit for the double helix
Why is DNA useful?
Each individual’s DNA is unique (except for ID twins)
Normally we all have 23 pairs
Only id twins will be exactly the same
What are the nucleotides?
organic molecules that are the building blocks of nucleic acids, such as DNA and RNA.
how many CODIS core STR Loci with chromosomal positions are there?
12 required testing points
What cell types contain DNA?
Blood
Semen
Saliva
Urine (Usually epithelial cells, not the urine itself. Cells fall to the bottom)
Hair
Teeth
Bone
Tissue
Who made it possible to bring DNA into evidence?
Sir Alec Jefferies
What was the first case Jefferies had anything to do with?
Colin Pitchfork
Transfer of DNA
Suspect DNA on victim’s body, clothing, belongings, etc.
Victim DNA on suspect’s body, clothing, belongings, etc.
Suspect or victim DNA on weapons, masks, cigarettes, drinking cups
Hit and run victim DNA on automobile
What can DNA tell us? What can it not tell us?
Can tell us the contributor, but not the intent/ how or when it was deposited
What is the process for Forensic Typing?
- Extraction
- Quantitation
- PCR Amplification of Multiple STR markers
What does STR stand for and what is it?
Short Tandem Repeats
PCR based-amendable to small sample size
Can perform multiple tests at one time
Relatively short analysis time
High power of discrimination
Looks at 24 locations of DNA with it’s own statistical significance
DNA profile comparison
Match= inclusion
No match= exclusion
Homozygous genes
Person has two copies of the same gene, one from mom, one from dad
Ex. 30
Heterozygous genes
Ex. 13/14
Two different characteristics inherited from the parents
What is the significance of the match on the sample screens?
Discrimination- the potential power of a system to differentiate between any two people chose at random
One forensically significant difference is an exclusion
The more regions of DNA match, less likely another individual would match at all regions
What is discrimination?
The potential power of a system to differentiate between any two people chose at random
Complex samples
Mixed profiles that can be resolved
Semen differential extraction to isolate sperm
They use a different technology to separate the female cells from the sperm with heat, etc.
What do Y-STRS do/ what are they used for/ what does it stand for?
Every male on the paternal line shares the same Y-STR profile
But beneficial when the DNA is mixed with female DNA
Paternal line focused
Mitochondrial DNA testing
maternal line DNA testing
What does SNP stand for? What is it?
Single nucleotide polymorphisms
What does accreditation in DNA ensure?
Personnel meet competency and proficiency standards
Techniques are validated and accepted
100% of casework is reviewed for technical
More
DNA analysis controls
Lab precautions
- Clean environment, use gloves at all times
- Separate areas of lab for different functions
- Known and unknown samples extracted at different times so attorneys can’t ask about contamination
Testing precautions
- Reagent blank
- Positive and negative control samples
SAMPLE RETESTING
What does CODIS stand for and what is it?
Combined DNA Index System
FBI created a situation where state labs across states and exchange and compare DNA profiles electronically
Became super beneficial with someone who was raping while in the military and he was in different states
Started in 1989 when DNA profiling was relatively new
- 2 major objectives
- To assist police in identification of suspects in violent crimes
- Increase effectiveness of forensic laboratories in DNA labs with frequency calibrations
- Get from lecture at around 1.5 hours
- Labs have to be local, state, or federal to get CODIS
What is local CODIS used for?
casework
What is state and national CODIS used for?
Convicted offender
- Some states have changed to be all arrested
- NY is not an all arrestee state
Casework
- Questioned samples we don’t know who they belong to
Missing persons
