1. Chapter 10 Advanced Concepts in DNA © 2012 Cengage Learning. All Rights Reserved

2. 2 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Introduction o Deoxyribonucleic acid (DNA)—the genetic material that makes each individual unique. Only identical twins have the same DNA DNA copies itself when cells divide DNA contains the blueprint for making proteins essential for life processes DNA is found in biological evidence DNA is individual evidence

3. 3 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Structure and Function (Obj 10.2) o Nucleotides—subunits of DNA Deoxyribose Phosphate group Nitrogenous base Adenine Thymine Cytosine Guanine

4. 4 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Structure and Function (Obj 10.2) o Adenine always pairs with thymine o Guanine always pairs with cytosine

5. 5 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Structure and Function (Obj 10.2) o Alleles— an alternative form of a gene for a certain trait. o An individual inherits two alleles for each gene, one from each parent.

6. 6 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Structure and Function (Obj 10.2)

7. 7 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved What Causes Variation in DNA? (Obj 10.2) o 99.5% of DNA is the same for everyone o 0.5% of DNA is what makes us unique o Homozygous—when two alleles are identical for a particular trait o Heterozygous—when two alleles are different o Marker—a sequence of DNA base pairs associated with a specific trait o Matching markers from two samples determines the likelihood of an individual being the same as the reference sample

8. 8 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved DNA Analysis Procedures (Obj 10.3, 10.4) o Method of extraction varies depending upon The type of biological evidence analyzed The amount of evidence available The type of cells present o Chelex Extraction Used when a small amount of biological evidence is available Sample placed in boiling water with Chelex beads The cells in the sample burst open to expose and preserve DNA

9. 9 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved DNA Analysis Procedures (Obj 10.3, 10.4) o Organic Extraction—removing biological evidence from materials (e.g., blood from bed sheets) o Differential Extraction—separates vaginal epithelial cells from sperm cells with a mild solution of phenol and chloroform

10. 10 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved DNA Fingerprinting o Fingerprinting has several steps Isolate and purify DNA Population genetics determines probability of another individual having the same profile http://stem-works.com/external/activity/178

11. 11 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved DNA Fingerprinting

12. 12 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved STR o Short Tendem Repeats—a short segment of DNA in which the same sequence of 2 to 6 base pairs is repeated many times o Easier and quicker to replicate o Repeating STR patterns are highly variable between individuals; therefore o Matching multiple STRs between individuals has a very low probability

13. 13 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved CODIS o Combined DNA Index System An FBI nationwide database Stores DNA fingerprints of individuals who have been convicted of certain crimes Open to forensic scientists to compare DNA fingerprints of suspects based on 13 core STR locations

14. 14 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved CODIS

15. 15 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Collecting DNA Evidence (Obj 10.5) o Biological samples Avoid contamination Retain original surface when possible Reference samples for comparative analysis o Stop degradation Protect sample from environmental exposure Remove moisture by drying out and freezing the sample

16. 16 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Collecting Biological Evidence o Examples Skin cells Blood Saliva Semen Hair Other possibilites?

17. 17 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Collecting Biological Evidence o Guidelines Never use bare hands Avoid sneezing and coughing Use clean protective gloves for each item collected Package each sample separately Air dry evidence located on objects; store in an envelope or paper bag, not plastic bags Establish a chain of custody

18. 18 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Collecting Reference Samples o Known samples taken from suspects and victims o Reference samples are compared to evidence collected from the crime scene

19. 19 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Testing for Blood, Semen, & Saliva o Presumptive tests used at the crime scene o Luminol is the most common method used to detect blood Sprayed on objects to find bloodstains Detects blood even when diluted o Chemicals and fluorescent dyes are used to visualize seminal fluid o For saliva, the Phadebas test or starch iodine test detects the presence of amylase

20. 20 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Mitochondrial DNA (mtDNA) Analysis o mtDNA is inherited from the mother o Easier to extract than nuclear DNA o Less likely to degrade o Each cell has hundreds of copies of mtDNA o Typically extracted from teeth, hair, bones o Take care to avoid altering this evidence for other analyses

21. 21 Forensic Science II: Advanced Concepts in DNA, Chapter 10 © 2012 Cengage Learning. All Rights Reserved Y-Chromosome Analysis o Passed down through paternal lineage o Beneficial for the following situations Sexual assault Missing person Genealogy o Does not provide individual evidence