DNA

Question 1

What is DNA?

Answer 1

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

Question 2

Why is DNA useful?

Answer 2

Each individual’s DNA is unique (except for ID twins)

Normally we all have 23 pairs

Only id twins will be exactly the same

Question 3

What are the nucleotides?

Answer 3

organic molecules that are the building blocks of nucleic acids, such as DNA and RNA.

Question 4

how many CODIS core STR Loci with chromosomal positions are there?

Answer 4

12 required testing points

Question 5

What cell types contain DNA?

Answer 5

Blood
Semen
Saliva
Urine (Usually epithelial cells, not the urine itself. Cells fall to the bottom)
Hair
Teeth
Bone
Tissue

Question 6

Who made it possible to bring DNA into evidence?

Answer 6

Sir Alec Jefferies

Question 7

What was the first case Jefferies had anything to do with?

Answer 7

Colin Pitchfork

Question 8

Transfer of DNA

Answer 8

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

Question 9

What can DNA tell us? What can it not tell us?

Answer 9

Can tell us the contributor, but not the intent/ how or when it was deposited

Question 10

What is the process for Forensic Typing?

Answer 10

1. Extraction
2. Quantitation
3. PCR Amplification of Multiple STR markers

Question 11

What does STR stand for and what is it?

Answer 11

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

Question 12

DNA profile comparison

Answer 12

Match= inclusion
No match= exclusion

Question 13

Homozygous genes

Answer 13

Person has two copies of the same gene, one from mom, one from dad
Ex. 30

Question 14

Heterozygous genes

Answer 14

Ex. 13/14
Two different characteristics inherited from the parents

Question 15

What is the significance of the match on the sample screens?

Answer 15

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

Question 16

What is discrimination?

Answer 16

The potential power of a system to differentiate between any two people chose at random

Question 17

Complex samples

Answer 17

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.

Question 18

What do Y-STRS do/ what are they used for/ what does it stand for?

Answer 18

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

Question 19

Mitochondrial DNA testing

Answer 19

maternal line DNA testing

Question 20

What does SNP stand for? What is it?

Answer 20

Single nucleotide polymorphisms

Question 21

What does accreditation in DNA ensure?

Answer 21

Personnel meet competency and proficiency standards
Techniques are validated and accepted
100% of casework is reviewed for technical
More

Question 22

DNA analysis controls

Answer 22

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

Question 23

What does CODIS stand for and what is it?

Answer 23

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

Question 24

What is local CODIS used for?

Answer 24

casework

Question 25

What is state and national CODIS used for?

Answer 25

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