1. Monday, 11/14/11 Objective: Do Now:
To understand how DNA evidence is used to solve crimes and determine paternity.
Do Now:
Why do they call this process “DNA Fingerprinting”?

2. Tuesday, 11/15/11 Objective: Do Now:
To understand how DNA evidence is used to solve crimes and determine paternity.
Do Now:
Which suspect’s DNA matches the crime scene? How do you know?

3. Wednesday, 11/23/11 Objective: Do Now:
To understand how DNA evidence is used to solve crimes and determine paternity.
Do Now:
What do restriction enzymes do?

4. Chapter 7 DNA Fingerprinting By the end of this unit you will be able to:
Explain how crime scene evidence is
collected and processed to obtain DNA
Describe how radioactive probes are used in DNA fingerprinting
Explain how DNA evidence is compared for matching
Explain how to use DNA fingerprinting to identify DNA from a parent, child, other relative, or a non-related individual

5. Introduction
Except for IDENTICAL twins, no two people on earth have the same DNA
DNA evidence has been used since the 1980’s to investigate crimes
Used to link/eliminate suspects
Used to identify victims
Used to establish paternity

6. History of Biological Evidence in Forensics
DNA fingerprinting
Also known as DNA profiling
Used with a high degree of accuracy
Biological evidence (skin, blood, saliva, urine, semen, and hair) is examined for the presence of inherited traits
This forensics laboratory techniques was originally developed for medical purposes
DNA can be extracted from a small about of evidence (a drop of blood or a single hair follicle)

7. The Function and Structure of DNA
DNA contains the genetic material of a cell
Contain directions for how to make proteins – gives organism their structure & function
Chromosomes are located in the nucleus of every cell (except RBC’s)
Chromosomes contain long DNA strands wrapped around proteins

8. Forensic Science: Fundamentals & Investigations, Chapter 7

9. The Function and Structure of DNA
Nitrogenous Bases—pairs of molecules that form the rungs of the DNA “ladder”
Four types of Bases
A (adenine)
C (cytosine)
G (guanine)
T (thymine)

10. The Function and Structure of DNA
Base-Pairing Rules
adenine (A) binds only with thymine(T)
cytosine (C) binds only with guanine (G)

11. How DNA is inherited ½ (23 chromosomes) from each parent
This results in one allele (form of a gene) from each parent

12. Genome Total amount of DNA in each cell
Each cell contains all the DNA but only some is used – allowing very different types of cells/tissues
Portions of DNA that are used are called exons. Unused portions (non-coding DNA) are called introns.
This is VERY important for DNA fingerprinting.

13. DNA Identification
Most DNA is the same in all humans but some variation exists allowing for identification
Polymorphisms: Non-coded DNA that contain unique patterns of repeated base sequences that that are unique to individuals
DNA Fingerprinting (Profiling) isolates and analyzes polymorphisms
DNA fingerprints appear as a pattern of bands on X-ray film.

14. DNA Profile
Due to unique polymorphisms each person will show a unique pattern!
Because they are unique they are called DNA fingerprints

15. DNA Profile Two types of repeating DNA sequences
Variable Numbers of Tandem Repeats (VNTR)
The number of repeats varies from person to person
9 to 80 bases (A, T, G, or C’s) in length
Example CATACAGAC repeats in code (CATACAGAC CATACAGAC CATACAGAC CATACAGAC)
Short Tandem Repeats (STR)
2 to 5 bases in length
Shorter lengths make STRs easier to use than VNTRs
Example GATA repeats in the code (GATA GATA GATA GATA GATA…)

16. DNA Profile Tissue Matching Inheritance Matching
STR’s are much shorter than VNTR’s and are becoming the preferred method of analysis
VNTR and STR data are analyzed for
tissue matching
inheritance matching
Tissue Matching
Two samples that have the same band pattern are from the same person
Inheritance Matching
Each band in a child’s DNA fingerprint must be present in at least one parent

17. DNA Profile - paternity test

18. DNA Profile - paternity test
Who is the father of Kid 1?
Kid 2?
How did you know?

19. DNA Profile – tissue match (crime scene)

20. DNA Profile – tissue match (crime scene)
Which suspect is guilty? Why did they have the boyfriend give a sample? They female cells?

21. DNA Profile – tissue match (crime scene)

22. DNA Population Databases
Population genetics:
the study of gene variations among groups of individuals
Analyze the probability of a random person with the same alternative form of a gene (an allele)
Can get specific information about race, eye color, blood type to narrow down suspect pool
Examples
Identifying the suspect in a crime
Identifying an alleged father in a paternity case

23. Sources of DNA
Biological evidence: examples include saliva, blood, skin, hair, seminal fluid
Individual evidence is capable of identifying a specific person.
Small amounts may be only trace evidence – but a little bit of DNA can be copied to make a larger testable amount
Polymerase chain reaction (PCR) technique generates multiple copies of DNA evidence

24. Collection and Preservation of DNA
Use disposable gloves and collection instruments
Avoid physical contact, talking, sneezing, and coughing in the evidence area
Air-dry evidence and put it into new paper bags or envelopes
Dry or freeze the evidence
Keep evidence cool and dry during transportation and storage

25. Preparing DNA Samples for Fingerprinting
Extraction
Cells are isolated from biological evidence such as blood, saliva, urine, semen, and hair
The cells are disrupted to release the DNA from proteins and other cell components
The DNA can be extracted from the cell nucleus

26. Preparing DNA Samples for Fingerprinting
Amplification
VNTR analyses—polymerase chain reaction (PCR) can be used to amplify the DNA that contains the VNTRs
STR profiles—restriction enzymes are unnecessary; PCR allows the amplification of the strands with STR sequences

27. PCR – DNA copy machine

28. Preparing DNA Samples for Fingerprinting
DNA is mixed with special proteins called restriction enzymes.
Restriction enzymes cut apart the DNA in specific places forming different sized fragments
Ex: EcoRI cuts DNA only at a GAATTC see diagram
PvuII cuts at CAGCTG
PvuII

29. Electrophoresis Overview
Forensic Science: Fundamentals & Investigations, Chapter 7

30. Preparing DNA Samples for Fingerprinting
Electrophoresis
DNA samples are placed in gels through which electronic currents are passed
DNA fragments line up in bands along the length of each gel

31. Electrophoresis
An electrophoresis apparatus running five sample of DNA
Arrows show the movement of the negatively charged DNA fragments through the gel matrix

32. Probes Humans have A LOT of DNA
To limit what we are looking at DNA probes are used
DNA probes
identify the unique sequences in a person’s DNA
are made up of different synthetic sequences of DNA bases complimentary to the DNA strand
bind to complimentary bases in the strand (see the fragmentary DNA bands above)
In most criminal cases, 6 to 8 probes are used

33. Analysis of DNA Fingerprints and Applications
DNA fingerprinting can
match crime scene DNA with a suspect
determine maternity, paternity, or match to another relative
eliminate a suspect
free a falsely imprisoned individual
identify human remains

34. Southern Blot/Probes Clarification
Humans could have 100’s of thousands!!
6 – 8 probes (sequences) are used for crime scene analysis

35. Summary
DNA contains the information needed for replication in a sequence of nitrogenous bases.
DNA analysis allows even a small sample of tissue to be identified with a single individual.
DNA contains, in non-coding regions called junk DNA, many repeated sequences that vary in number between individuals.
These differences between individuals can be used to produce a DNA fingerprint for an individual.

36. Summary
Polymerase chain reaction (PCR) for DNA amplification has largely eliminated the problem resulting from the tiny samples usually available.
DNA evidence must be collected carefully to avoid contamination with other DNA.
DNA analysis involves extraction, electrophoresis, and visualization.
DNA profiles are kept by police agencies in electronic databases.

37. Gel Electrophoresis of Food Coloring - LAB
You must wear goggles at all times
Be patient and take turns with micropipettes
Follow all directions
Be aware that we are using electricity to separate colors – be cautious

38. Centrifuge
Place all samples into centrifuge and turn on for about 10 seconds
All your liquid should be at the bottom of your tube

39. How to Use a micropipette
Use the first stop to “suck up” sample, and second stop when inserting in gel!
Eject tips into beaker – use a new tip for each color!

40. Pipette coloring into wells in the middle of your gel – once it has been covered with TBE
DO NOT poke through the bottom – if you do redo that color in another well

41. Carefully slide cover onto chamber, make sure unit is turned OFF and plug in black to black – red to red
Turn on and make sure voltage is at 110V – watch your gel “run”

42. DNA Detectives Lab

43. DNA Detectives – Day 1
Read procedure and be prepared to work on questions for tomorrow.
Part I will be completed for you – We will begin with Part II (Method 2: Submarine)
We will load and “run” gels today.
Make a Ziploc bag with your names on - so that gel can be saved for staining tomorrow!