1. Forensic Analysis of DNA

2. DNA Unlike hair and serology, DNA is one of the rare pieces of evidence that can be statistically linked to a single person. Found in all body tissues and fluids ◦Greater identification potential than fingerprints

3. DNA Molecule Deoxyribonucleic Acid (DNA) ◦genetic molecule that makes up chromosomes ◦encodes the instructions for when and how to make proteins for living organisms ◦All cells have DNA (bacterial cells to complicated cells)

4. DNA Molecule Sides of DNA are made of phosphates and sugars Rungs are made out of nucleotides Made up of ACGT Less than 1% of DNA is similar in humans Scientists have figured out genetic repeats and call them variable number tandem repeats (VNTRs), which are used to type DNA Single person can be linked to a DNA profile due to VNTRs

5. DNA and Inheritance Nuclear DNA ◦Found in nucleus ◦23 chromosomes from each parent ◦All cells contain the same nuclear DNA (important to forensics) ◦Each person has a unique set of DNA, unless identical twins ◦Closer related to a person, the more DNA have in common Mitochondrial DNA ◦Located in mitochondria ◦Inherited completely from mother ◦All siblings have identical mitochondrial DNA

6. DNA and Forensics Scientist knew it could be found in body cells (living or dead) potential source of nuclear or mitochondrial DNA Early DNA research involved trying to figure out the best source of crime scene DNA ◦Blood, semen and body tissue Scientist eventually figured out that DNA is left behind on other things: ◦Cigarette butts, licked envelope seals, hair follicles and latex gloves Fresh tissues yield more DNA than older tissues due to DNA degrading overtime ◦Analyst may be able to get mitochondrial DNA out of an old sample even if nuclear DNA is too degraded

7. DNA and Crime Scene Forensics Anything wet, such as a blood covered piece of cloth, has to be air dried put in a container slightly open to stop moisture buildup. Kept at low moisture to help prevent the growth of bacteria and fungi ◦Bacteria and fungi have their own DNA Contamination can be unavoidable ◦Body decomposing in a lake ◦DNA analyst can figure out how to minimize cross contamination with the many creatures that live in bodies of water once body arrives in the morgue

8. DNA and Crime Scene Forensics If DNA on glass or chewed gum then entire sample should be sent to the lab If sample not transportable, then take a portion of it to the lab that contains the questioned DNA Technicians have to be careful with DNA ◦Infectious body fluids ◦Contamination of the sample with their own DNA ◦Hair, dandruff, skin cells or saliva etc.

9. DNA and Crime Scene Forensics Reference sample ◦Known sample ◦Usually taken with a buccal swab DNA samples taken from dead person to identify person ◦Reference sample may be taken from a toothbrush

10. DNA Profiling Scientists use sequence and length of polymorphisms to develop someone’s DNA profile

11. RFLP Restriction fragment length polymorphism ◦First successful method ◦Restriction enzyme cuts DNA at polymorphic places to create DNA fragment that differ between 2 people ◦Gel electrophoresis sorts the RFLP fragments by size creating a DNA fingerprint ◦Requires a large sample and results are no compatible with major DNA computer databases ◦RFLP has been replaced

12. DNA Profiling Polymerase chain reaction (PCR) ◦Developed in 1983 ◦Mass producing copies of DNA ◦Amplifies a small sample of DNA so that there is plenty of it to analyze in a forensic case

13. DNA Profiling Short Tandem Repeat (STR) ◦replaced RFLP ◦Uses PCR and some of the principles of RFLP ◦Quicker than RFLP and does not need as much DNA ◦Profiles generated are sets of numbers that can be entered into CODIS DNA advancement ◦Looking at DNA from sex chromosome to determine if DNA is from a woman or a man.