1. DNA Indispensable Forensic Science Tool

2. Understanding DNA-1 What is it? Deoxyribonucleic Acid-DNA Located in the nucleus of every cell in your body Contains hereditary information Allows for definitively linking semen, blood, hair, and tissue to a single individual.

3. Understanding DNA-2 What is it? Structure of DNA ◦Made up of the subunit “nucleotides” ◦Nucleotides have 3 parts:  Sugar (deoxyribose)  Phosphate group  Nitrogen Base (A, T, C, and G) ◦ A-adenine pairs with T-thymine ◦ C-cytosine pairs with G-guanine See figure 9-1

4. Understanding DNA-3 What is it? Complementary Base Pairing Figure 9-2 shows complimentary base pairing in a strand of DNA. Practice the following: write the complementary bases for the strand T-A-T-T G-T-A-A G-T-C-A

5. Understanding DNA-4 What is it? DNA at Work DNA is involved in the direct process of making proteins Proteins are made up of amino acids. There are thousands of proteins, but only 20 amino acids that exist. DNA sequences determine the protein that is made. The sequence of amino acids determines the shape of a protein and the shape determines its job.

6. Understanding DNA-5 What is it? Hemoglobin is found in our RBCs It is a protein made up of a sequence of amino acids. If a mutation occurs in the DNA sequence that codes for the protein hemoglobin an abnormal protein can be made Ex. Sickle cell hemoglobin

7. Understanding DNA-6 What is it? Normal Hemoglobin Sickle-cell hemoglobin valine histadine leucine threonine proline glutamate valine histadine leucine threonine proline valine glutamate

8. Understanding DNA-7 What is it? How DNA relates to protein: ◦Normal Hemoglobin DNA sequence and amino acid sequence ◦Normal Hemoglobin ◦DNA seq: C-C-T G-A-G G-A-G ◦AA seq: ◦Abnormal Hemoglobin ◦DNA seq: C-C-T G-T-G G-A-G ◦AA seq: proline glutamate proline glutamatevaline

9. Replication of DNA-1 Process of replication Replication: synthesis of new DNA from existing DNA ◦1. Helicase unzips the 2 DNA strands ◦2. DNA polymerase lays down new DNA nucleotides ◦3. DNA strand is proof read by DNA polymerase ◦RESULT: 2 identical strands of DNA each containing one pre-existing strand and one new strand.

10. Replication of DNA-2 Polymerase Chain Reaction Copying of DNA outside of a living cell. ◦DNA is broken into small pieces found at a crime scene. ◦DNA polymerase is used to copy the DNA using a DNA Thermal Cycler ◦This opens up exciting doors in the field of forensics-sample size no longer being a limitation.

11. Replication of DNA-3 Polymerase Chain Reaction Steps of PCR ◦1. Heating: Heat the DNA strands to 94 C. Causes separation of strands ◦2. Cooling: Add primers to separated strands and combine lowering temp to 60 C. ◦3. Rebuilding: Add DNA polymerase and free nucleotides. Heat temp to 72 C and the replicating begins. ◦28-32 cycles are usually done to yield 1 billion copies (2min. Per cycle)

12. DNA Typing w/ Tandem Repeats-1 RFLP Tandem repeats are repeating sets of nucleotides that fill space b/w coding regions of DNA. Do not code for a gene. Useful in distinguishing one individual from another via DNA typing.

13. DNA Typing w/ Tandem Repeats-2 RFLP RFLP are different fragment lengths of base pairs that result from cutting a DNA molecule with restriction enzymes. ◦Electrophoresis ◦Length differences in RFLPs allow us to distinguish one person from another. ◦Fragments are separated through migration on a medium under the influence of electricity. ◦Smaller fragments move faster than larger fragments.

14. DNA Typing w/ Tandem Repeats-3 RFLP Hybridization ◦After electrophoresis the strands are chemically treated to cause separation. ◦Strands are transferred to nylon sheet. ◦Nylon sheet is treated w/ radioactive labels.

15. DNA Typing w/ Tandem Repeats-4 RFLP DNA Typing w/ RFLP ◦Nylon sheet is placed against X-ray film and exposed for several days. ◦Radioactive debris strike the film. Bands appear where the debris struck. ◦Process seen in Fig 9-8

16. DNA profile

18. Short Tandem Repeats (STRs)-1 Multiplexing STR-A region of a DNA molecule that contains short segments of three to seven repeating base pairs. A technique that simultaneous detects more than one DNA marker in a single analysis-multiplexing (analyzing a combination of STRS)

19. Short Tandem Repeats (STRs)-2 DNA Typing with STRS The more STRs characterized, the smaller the % of the population from which a combination of STRs can emanate. With STR, as little as 125 picograms of DNA is required for analysis-1/100 the amount normally required for RFLP analysis

20. Short Tandem Repeats (STRs)-3 Capillary Electrophoresis Used to separate STRs. Typically carried out on flat gel-coated electrophoretic plate. To reduce time can be carried out in a thin glass column. ◦Fig 9-14

21. Short Tandem Repeats (STRs)-4 Sex ID Using STRs Focus is on amelogenin gene located on both the X and Y chromosome. ◦Actually the gene for tooth pulp ◦Smaller by 6 bases in the X chromosome than in the Y. Y-STRs ◦STRs found on the Y chromosome. ◦More than 20 different Y-STR markers have been identified. ◦Useful when multiple males are involved in a sexual assault.

22. Short Tandem Repeats (STRs)-5 Significance of DNA Typing Has become essential and a basic investigation tool in law enforcement communities. Has helped to exonerate those wrongly convicted and imprisoned ◦Fig 19.5

23. Mitochondrial DNA Located outside cells nucleus, inside the mitochondria. Inherited from your mother. Typically used for samples like hair where STR analysis might not be possible 2 regions of mitochondrial DNA are sequenced for forensic typing purposes ◦HV1 and HV2 ◦Fig 9-16

24. CODIS- Combined DNA Index System Computer software program developed by the FBI Maintains local, state, and national databases of DNA profiles from: ◦Convicted offenders ◦Unsolved crime-scene evidence ◦Missing people

25. Collection and Preservation of Biological Evidence for DNA Analysis Collection of Biological evidence-1 Evidence is photographed Evidence is handled w/ very little personal contact. ◦Assumed to be infectious Safety precautions are taken: ◦Gloves are worn ◦Face masks ◦Shoe covers ◦Coveralls

26. Collection and Preservation of Biological Evidence for DNA Analysis Packaging of Evidence-2 NOT packaged in plastic or airtight containers due to moisture. Articles are packaged separately in a paper bag or in a well-ventilated box. Refrigeration is necessary to preserve evidence.

27. Collection and Preservation of Biological Evidence for DNA Analysis Obtaining Refrence Specimens-3 Buccal swabs are the easiest way to obtain a reference sample. Cotton swabs are inserted in the subjects mouth and the cheek is vigorously swabbed. This results in the transfer of cells from the inner cheek to the cotton swab.

28. Collection and Preservation of Biological Evidence for DNA Analysis Contamination of DNA Evidence-4 Introduction of foreign DNA (sneezing or coughing) can contaminate samples. Precautions: ◦Change gloves ◦Collect substrate controls ◦Use forceps to pick up small samples ◦Package items in well ventilated containers.