1. The Indispensible Forensic Science Tool
Chapter 9: DNA
The Indispensible Forensic Science Tool

2. If you were on the jury…….
Would you have enough knowledge about DNA to understand what the prosecution and or defense was presenting in court?
Would you have enough knowledge to make a good judgment about guilt or innocence based on DNA evidence?
… or would it be another
O.J. Simpson case????

3. Polymer
A polymer is a large molecule made of many repeating smaller units called monomers.
Monomer

4. Chromosome
Nucleus
When forensic evidence includes DNA evidence, specifically what did forensic technologist possibly collect at the scene?
Human Body Cell
DNA
Gene

5. Sources of DNA Evidence
Can be found in all body cells
Blood
Semen
Saliva,
Urine
Hair roots
Teeth
Bone
Muscle Tissue
Most abundant in our buccal (cheek) cells
Blood is 99.9% red blood cells that have no nuclei; and therefore, no nuclear DNA
DNA obtained from blood comes from white blood cells

6. ….is to direct the building
The job of DNA
….is to direct the building
of proteins.

7. DNA Replication

8. Methods of making more copies of DNA:
Recombinant DNA
Uses bacteria to copy fragments of DNA
Use to make vaccines
Not useful in forensic DNA analysis…..WHY???
Polymerase Chain Reaction (PCR)
Uses heat, primers, and enzymes to copy strands of DNA

9. Recombinant DNA Vaccines are made this way
Bacteria are used because they reproduce rapidly, making more of the newly inserted DNA as they do.
Vaccines are made this way
Recombinant DNA
“Recombine” two piece of DNA from 2 different sources

10. The polymerase chain reaction (PCR) is a biochemical technology used to amplify a single or a few copies of a piece of DNA.
It generates millions of copies of a particular DNA sequence in just two minutes.

11. What is DNA Typing? Also known as DNA Fingerprinting
Method in which DNA is converted into a series of bands that ultimately distinguishes each individual.
Only one-tenth of a single percent of DNA (about 3 million bases) differs from one person to the next. Scientists use these regions to generate a DNA profile of an individual.

12. Process of DNA Typing? Method consists of three basic steps:
Cutting DNA into small pieces
Separating those small pieces
Completing a process that makes these small pieces visible

13. DNA Fingerprinting

14. DNA Typing: aka DNA Fingerprinting

15. Each probe only recognizes a DNA sequence.
Multiple probes will be added to single sample so that each of the DNA segments will be visible.

16. RFLP vs. STR 2 types of DNA typing:
Restriction Fragment Length Polymorphism (RFLP)
Uses a sequence of nitrogenous bases to make bands on the electrophoresis gel
Can’t use PCR because the sequence is too long
Can take up to 10 weeks to complete

17. RFLP vs. STR 2 types of DNA typing: Short Tandem Repeats (STR)
Uses a sequence of 3-7 nitrogenous bases to make bands on the electrophoresis gel
PCR is used with these short sequences
Can be completed within about 3 days

18. AGCT AGCT AGCT AGCT 4 Repeats
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Short Tandem Repeats STRs Counting the number of repeats by size comparison
Largest
AGCT AGCT AGCT AGCT 4 Repeats
AGCT AGCT AGCT Repeats
AGCT AGCT Repeats
AGCT Repeat
Smallest

19. Because the DNA can be replicated in the laboratory for a STR process, it isn’t necessary for forensic technicians to collect a large sample of DNA from the actual crime scene.

21. Types of DNA Nuclear Mitochondrial found in the nucleus
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Nuclear
found in the nucleus
constitutes 23 pair of chromosomes inherited from both parents
each cell contains only one nuclei
Mitochondrial
found in the cytoplasm
is inherited only from mother
each cell contains hundreds to thousands of mitochondria
can be found in skeletal remains

22. Mitochondrial DNA Analysis of mtDNA is more: difficult time consuming
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Mitochondrial DNA
Analysis of mtDNA is more:
difficult
time consuming
costly than nucleic testing of DNA
Only used when nuclear DNA typing is not possible

25. 1994
Vietnam unknown soldier identified using mitochondrial DNA

26. Present Work in DNA CODIS--Computer Based DNA Information System
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CODIS--Computer Based DNA Information System
A data base of DNA profiles of individuals convicted of sex crimes and other violent crime
Innocence Project
Group of college law students work on cases where DNA may prove innocence (or guilt)
Since the late 1980’s, DNA technology has been available. People, as a result, have been reopening cases and testing the evidence for DNA. Some have been exonerated because their DNA did not match.

27. FBI’s CODIS DNA Database
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FBI’s CODIS DNA Database
Combined DNA Index System
Used for linking serial crimes and unsolved cases with repeat offenders
Launched October 1998
Links all 50 states
Requires >4 RFLP markers
and/or 13 core STR markers

28. The Future Greater automation of the DNA typing process
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The Future
Greater automation of the DNA typing process
Use of SNP’s--single nucleotide polymorphism which measures a one nucleotide change or difference from one individual to another.

29. Before and After
In a paragraph, describe how the process of DNA fingerprinting prior to 1990’s was different to the techniques used since that time.
Page 317 may be useful to you
Make sure to use the terms we have covered concerning these processes.