1. Lecture 2: Sources of DNA Evidence

2. DNA Biological evidence containing DNA Blood Semen Saliva Hair Bone Teeth Touch/trace 2

3. Most cells contain DNA Digital information molecule Information carried in sequence (A,T,C,G) Mutations change the sequence over time Different forms = alleles In animals, two types Nuclear Mitochondrial Forensic biologists use both 3

4. Nuclear DNA Inherited from both parents Two copies per cell Pristine (full profile): Fresh materials (semen, saliva, blood, bone); rooted hairs E.g. Semen stain taken 12 hours after rape PD in the quintillions Compromised (partial profiles) or completely degraded (no profile): Aged or damaged materials; hair shafts E.g. Saliva on a cigarette butt exposed to rain for 1 week PD reduced based on level of degradation 4

5. Mitochondrial DNA Found inside the cells mitochondria Powerhouses that provide the cells energy Thousands of copies/cell Inherited only from the mother Can be obtained from most biological materials (fresh or old) E.g. Skull found in a field; body dumped 2 years prior Usually possible to get full profile PD low (1 in a few hundred is typical) All maternally-linked relatives carry the same mtDNA 5

6. Nuclear DNA is preferred due to high PD BUT… Mitochondrial DNA may be the only option for some samples And its much better than nothing! The fewer cells and/or the more compromised the evidence, the less likely you can get a nuclear DNA profile 6

7. Blood Often shed at violent crime scenes Is usually the victims blood Look for victims blood on suspects skin, shoes, or clothing Consists of erythrocytes (red blood cells), leucocytes (white blood cells), and platelets Nuclear DNA obtained from leucocytes; erythrocytes and platelets lack nuclei and DNA 7

8. 8 Nucleated leukocyte surrounded by enucleated erythrocytes

9. Semen Very common in sexual assaults Recovered from skin, vagina, oral cavity, rectum of victims Condoms = perfect evidence item Rich source of DNA Sperm are little bags of DNA (more on this later…) Persists inside/on victims for up to 72 hours Persists on inanimate objects up to many years E.g. Semen stain on carpet 9

10. Saliva Common in sexual assaults Recovered from skin, labia, peri-oral regions on victim Other common sources: Cigarette butts Back of envelopes and postage stamps Rims of beer cans, drinking glasses Contains lots of bacteria If evidence not dried and stored properly, will quickly degrade 10

11. Hair Root Shaft Medulla Cortex Cuticle Grows at approximately 0.3mm per day Three phases: Anagen phase- growing phase (nuclear DNA) Catagen phase- follicle becomes inactive (nuclear DNA) Telogen phase- growth cycle ends (mtDNA only) 11

12. 12 A hair follicle

13. 13 Cross section of a hair shaft

14. 14 Telogen hairs lack roots People shed more than 200 telogen hairs per day Look inside caps or on clothing or furniture Hairs with rooted must be plucked or pulled out by force Look in the hands of a victim after a struggle Procedure: Microscopy to identify phase Choose appropriate DNA testing method

15. 15 Hair morphology: Differences in human hair color

16. 16 Hair morphology: Absence (above) or presence (below) or medulla

17. 17 Hair morphology: Distinct cuticle layering patterns

18. Bone Spongy Rich source of cells and DNA but… Degrades quickly after death Good source of nuclear DNA Compact Fewer cells than spongy bone but… Degrades less quickly after death Good source of mitochondrial DNA Mass fatalities (e.g. 911) Sanding prior to DNA analysis to prevent comingling of remains 18

19. Bone Rate of degradation of human remains varies greatly with environmental conditions Soft tissue is lost Bones are more stable Mass Fatalities-identify victims 19

20. Teeth Dentin- no cells Pulp Cavity Contains lots of cells and DNA if tooth is fresh Root Contains root canal with cells and DNA if tooth is fresh 20

21. In addition to DNA analysis, teeth can be used to: Identify a person Characteristics of teeth Alignment Overall structure X-rays Compare suspects with bite marks on victim What else might be present on a bite mark that could help identify a criminal? 21

22. Touch/Trace DNA First described into 1997: DNA Fingerprints from Fingerprints (Nature article) Sources: Surface skin cells Cells transferred onto hands from eyes and mouth Low levels; usually partially degraded Often contains DNA from more than one person DNA mixtures Difficult to interpret (is it really related to the crime?) E.g. Cell phones, keyboards, doorknobs, clothing 22

23. 23

24. 24 Primary Biological Evidence in Cases Reviewed by Dr. Ballard in 2012