1. DNA

2. General DNA Information
Double helix—two coiled DNA strands
Composed of nucleotides—units containing
sugar molecule (deoxyribose),
phosphate group
nitrogen-containing base
adenine
deoxyribose
PO4

3. General DNA Info
In humans, the order of these bases is 99.9% the same.
Four bases
Adenine
Cytosine
Guanine
Thymine
Bases always pair
A to T and G to C

4. Where Is DNA Found?
Genes are portions of DNA that code for specific proteins
DNA is found in all nucleated body cells—white blood cells, semen, saliva, urine, hair root, teeth, bone, tissue
Most abundant in buccal (cheek) cells
Red blood cells have no nuclei; and therefore, no nuclear DNA

5. Types of DNA Nuclear Mitochondrial found in the nucleus
constitutes 23 pairs 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

6. Mitochondrial DNA Analysis of mDNA is more:
rigorous
time consuming
costly than nucleic testing of DNA
mDNA is constructed in a circular or loop

7. Polymerase Chain Reaction
Technique used for making copies of a particular part of DNA
This can be valuable when the amount of evidence is minimal.
Millions of copies of DNA can be made from a single speck of blood.

8. PCR The outcome is a doubling of the number of DNA strands.
The cycle is typically 25 to 30 times, yielding more than one million copies of the original DNA molecule.
Each cycle takes less than 2 min from start to finish.

9. PCR Procedure
1) Heat the DNA strands, causing the strands to separate (unzip).
2) Cool the mixture and add a primer, a short sequence of base pairs that will add to its complementary sequence on the DNA strand.
3) Finally, add a DNA polymerase and a mixture of free nucleotides to the separated strands.

10. PCR Animation
PCR Animation

11. Electrophoresis Separates DNA fragments by length
Longer strands move through the gel more slowly
The smaller, lighter molecules will move the furthest on the gel.

12. Electrophoresis
Your restriction fragments will be different lengths than someone else’s restriction fragments
Every individual’s electrophoresis results look different because everyone has unique DNA sequences

13. Electrophoresis

14. Short Tandem Repeats (STRs)
Shorter than restriction fragments from PCR
More easily recovered from the often degraded and limited quantities of DNA typically found in evidence. 13

15. Short Tandem Repeats (STRs)
The FBI uses 13 core STRs for identification of Americans. 14

16. Short Tandem Repeats (STRs)
For all 23 PAIRS of chromosomes, 1 is from mom, and 1 is from dad. 15

17. Short Tandem Repeats (STRs)16

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

19. How to Collect DNA Evidence
1. Wear disposable gloves and change them often.
2. Use disposable instruments for handling each sample.
3. Avoid touching the area where you believe DNA may exist.
4. Avoid talking, sneezing, and coughing over evidence.
5. Avoid touching your face, nose, and mouth when collecting and packaging evidence.
6. Air-dry evidence thoroughly before packaging.
7. Put evidence into new paper bags or envelopes.
8. If wet evidence cannot be dried, it may be frozen.

20. Chimeras Rarely, people can have 2 different sets of DNA
Can be caused by a twin dying early in utero
Resultantly, can cause 2 blood types and different DNA in sex cells and other cells
Lydia Fairchild tested as not the biological mother of her children

21. Chimeras & Bone Marrow Bone marrow transplants can cause chimerism
New bone makes blood cells of original donor in new person’s body
Alaskan case where DNA taken matched a person in jail. He had donated bone marrow to his brother, who now had his brother’s DNA in his body.