1. DNA Fingerprinting

2. DNA Fingerprinting Applications
To link a suspect to a crime scene and for criminal exonerations.
O.J. Simpson and Colin Pitchfork
I.D. Missing persons or Dead Person.
Link a suspect to an event.
Clinton – Lewinsky Scandal
Paternity Cases.

3. DNA Fingerprinting Applications
DNA fingerprinting is routinely used to test samples of blood, hair root, saliva and other bodily fluids.

4. DNA Fingerprinting
Why is DNA an Indispensable Tool in Forensics Science?
Study into the structure of the human genome has led
to the discovery that portions of DNA structure of
certain genes are as unique to each individual as fingerprints.

5. What is DNA?
In 1953 James Watson & Francis Crick discovered the structure
Deoxyribonucleic Acid – DNA.
Double Helix Structure
It is found in the nucleus of all living cells, with the exception of
Red Blood Cells.

6. What is DNA?
A person has 46 chromosomes, over 100,000 genes, 3 billion bases of DNA.
Each leg of the ladder in the double helix consists of alternating
sugar and phosphate units.
The nucleotide bases consist of the following:
Adenine (A) which pairs with
Thymine (T)
Cytosine (C) which pairs with
Guanine (G)

7. What is DNA? Replication of a single strand of DNA
A T A G C C A A C C A A T A T C G
G T T G G T T

8. What is DNA?
The order of the bases in a molecule of DNA provide instructions used to build proteins.
A piece of DNA that contains all the information needed to build one protein is called a gene.

9. What is DNA Fingerprinting?
In 1985 an English geneticist, Alec Jeffreys, was studying inherited variation within genes and among individuals.
He studied a genetic peculiarity known as the intron. Introns are sequences of “junk” DNA that do not code for a specific protein.
He noticed that some introns are made up of the same DNA base pair sequences and that the number of repetitions varies from person to person.

10. DNA Fingerprinting Techniques
RFLP
Restriction Fragment Length Polymorphisms – RFLP are the repetitive
intron fragments
How RFLP works:
DNA from several individuals was “cut” with a restriction enzyme.
The “cut” DNA is sorted by size.
RFPL animation

11. DNA Fingerprinting Techniques
RFLP (continued)
Disadvantages of RFLP
Advantages of RFLP
Expensive.
Very confident in results
example:
Using RFLP on a sample of
blood from the O.J. Simpson
murder trial said the chances
someone other than Simpson
left their DNA at the crime
scene was 1 in 6 Billion.
Time consuming.
Labor intensive
Requires a large sample size.

12. DNA Fingerprinting Techniques
PCR
Polymerase Chain Reaction – PCR.
A technique used to “copy” DNA.
Can be used with minute amounts of DNA.
Uses DNA’s natural replication process to multiple sample size.
PCR animation

13. DNA Fingerprinting Techniques
PCR (continued)
Disadvantages of PCR
Advantages of PCR
Results are not as impressive
as RFLP.
Small sample size needed.

14. DNA Fingerprinting The Power of DNA Fingerprinting
Several drops of O.J. Simpson’s blood were found
at the Nicole Brown-Simpson and Ronald Goldman
crime scene. Both RFLP and PCR tests were performed. Here are the
official results:
PCR (3 Drops of Blood were tested)
1/240,000 chance blood belonged to someone other than O.J. Simpson.
RFLP (2 Drops of Blood were tested)
Drop #1: 1/170 Million chance blood belonged to someone other than O.J. Simpson.
Drop #2: 1/57 Billion chance blood belonged to someone other than O.J. Simpson.
Source: Criminalistics, An Intro to Forensics Science, Richard Saferstrein

15. DNA Fingerprinting
A picture of DNA fingerprinting

16. DNA Fingerprinting Mitochondrial DNA
Another structure in the cell that contains DNA is the
mitochondria.
Each cell contains thousands of
mitochondria, each containing several
Loops of DNA.
Unlike nuclear DNA, this DNA is only
inherited from your mother.
This makes any individual with the same
maternal lineage indistinguishable.

17. DNA Fingerprinting How DNA is used to determine Paternity
DNA fingerprinting can be used to determine a child’s parents.
We know you receive 50% of you nuclear DNA from mom, and
the other 50% from dad.

18. Interpret the results of the following
DNA Fingerprinting
Interpret the results of the following
DNA fingerprints
Both daughter 1 and son 1 share
genes with mom and dad, while
daughter 2 has genes of mom but
not the dad, and son 2 does not
share genes with either parent.

19. CODIS is an acronym for:
What is CODIS?
CODIS is an acronym for:
Combined DNA Index System
Administered by the FBI, system which stores DNA of
certain convicted felons.