1. DNA Analysis
Forensics Chapter 11

2. DNA
DNA “fingerprinting” is a common way to identify people by their unique genetic code
It is currently being used to identify the perpetrator in a crime, to identify fathers in paternity cases, and to identify unknown remains in mass disasters and other situations
DNA is in every nucleated cell of the human body and can be extracted from blood, semen, urine, bone, hair follicles, and saliva.

3. Biological Aspects of DNA
A basic functional and structural element of all living things is the cell
Cell functions on its own, as in a red blood cell, or in groups, as in tissues or organs
Chromosomes that are inherited from both parents, are long-chain DNA molecules that are tightly bound in a specific structure
Human body has approx. 35,000 genes, which are simply portions of the DNA the code the information required to make specific proteins
These proteins determine human traits and functions
Genes have a specific code for a specific body function, are the fundamental unit of heredity, and determine traits of organisms

4. Biological Aspects of DNA
DNA= deoxyribonucleic acid and is a long-chain molecule made of four nitrogenous bases that are paired and held together with hydrogen bonds and a sugar-phosphate backbone
Adenine pairs with Thymine; Cytosine pairs with Guanine
Structure determines function
Ability to replicate itself
Structure= double helix

5. Biological Aspects of DNA
Average DNA molecule contains approx. 100 million nucleotide groups
In humans, the order of these nucleotide bases is 99.9% the same
The unique sequence of the other 0.1% makes each human one of a kind (except in identical twins, who have the same DNA)
The sequence of these bases is a code for specific amino acids to combine to make specific proteins
The sequence of the nucleotide bases is what determines the proteins that will lead to specific growth, functions, and reproduction

6. Forensic Uses of DNA
Blood and bodily fluids are the most common evidence that forensic scientists use for testing DNA
Blood is made up of RBCs that carry oxygen throughout the body; plasma, the fluid that carries the cells; platelets, which facilitate clotting; and WBCs, which defend the body against infection
RBCs do not contain nuclei (means no DNA)
WBCs contain nuclei (scientists want this!!)
Polymerase Chain Reaction (PCR) is used to make copies so DNA can be tested

7. Forensic Uses of DNA
DNA fingerprinting can be useful for many purposes:
To identify potential suspects whose DNA may match evidence left at crime scenes
To clear persons wrongly accused of crimes
To identify crime and catastrophe victims
To establish paternity and other family relationship
To match organ donors with recipients in transplant programs

8. Forensic Uses of DNA
Samples collected from a crime scene are examined to determine whether the sample is appropriate for DNA analysis…therefore, it must be properly prepared
1. removed from object
2. extracted from the cell (DNA must be isolated- no fats, proteins, or carbohydrates)
3. enzymes used to release DNA from chromosomal packaging..then it’s ready! 

9. RFLP Analysis for DNA Fingerprinting
RFLP- restriction, fragments, lengths, polymorphism
DNA is cut into smaller pieces using restriction enzymes then the sample is run through electrophoresis, which separates the fragments according to size.
Four main procedures in DNA fingerprinting
Isolation of the DNA to separate the DNA from the cell
Cutting with a restriction enzyme to make shorter base strands
Sorting the segments by size, using an electrophoresis procedure
Analyzing the resulting print by identifying specific alleles

10. Statistical Analysis in DNA Fingerprinting
The DNA molecule is hundreds of thousands of base pairs long
Think: what are the chances of someone else having the same size fragment?
We don’t care if the sequence is the same, only that the fragments are the same length.

11. PCR and DNA Fingerprinting
When there is little evidence to work with, PCR is used because it can make many copies in a short period of time
Steps in PCR
Separation
Adding primer (begins replication process)
Synthesis of new chain

12. STR: Short Tandem Repeats
Example: GATAG ATAGATAGAT AGATAGATAG
Found on every chromosome and can easily be amplified
Benefits to DNA analysis
Takes less time
Smaller sample size
Exclusionary…eliminates more people faster!
Allows for cross jurisdiction verification

13. Mitochondrial DNA
Another structure in the cell that contains DNA is the mitochondria
Mitochondria are the powerhouses of the cell
Each cell contains thousands of mitochondria, each containing several loops of DNA
mDNA is inherited from only the mother
This makes any individual with the same maternal lineage indistinguishable if mDNA is used for analysis
Techniques scientists use to characterize mitochondrial DNA are significantly more sensitive than the techniques for profiling nuclear DNA…but it’s more expensive
FBI has only a few labs that will do mDNA testing and there are VERY strict limitations to the cases they will accept.