Embed Size (px)
Citation preview
Monday, 11/14/11
o Objective:• To understand how DNA evidence is used to
solve crimes and determine paternity.
o Do Now:• Why do they call this process “DNA
Fingerprinting”?
Tuesday, 11/15/11
o Objective:• To understand how
DNA evidence is used to solve crimes and determine paternity.
o Do Now:• Which suspect’s DNA
matches the crime scene? How do you know?
Wednesday, 11/23/11
o Objective:• To understand how
DNA evidence is used to solve crimes and determine paternity.
o Do Now:• What do restriction
enzymes do?
Chapter 7 DNA Fingerprinting By the end of this unit you will be able to:
o Explain how crime scene evidence is collected and processed to obtain DNA
o Describe how radioactive probes are used in DNA fingerprinting
o Explain how DNA evidence is compared for matching
o Explain how to use DNA fingerprinting to identify DNA from a parent, child, other relative, or a non-related individual
IntroductionIntroduction
o Except for IDENTICAL twins, no two people on earth have the same DNA
o 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
History of Biological History of Biological Evidence in Forensics Evidence in Forensics
o DNA fingerprinting • Also known as DNA profiling• Used with a high degree of accuracy
o Biological evidence (skin, blood, saliva, urine, semen, and hair) is examined for the presence of inherited traits
o This forensics laboratory techniques was originally developed for medical purposes
o DNA can be extracted from a small about of evidence (a drop of blood or a single hair follicle)
The Function The Function and Structure of DNA and Structure of DNA
o DNA contains the genetic material of a cell
o Contain directions for how to make proteins – gives organism their structure & function
o Chromosomes are located in the nucleus of every cell (except RBC’s)
o Chromosomes contain long DNA strands wrapped around proteins
Forensic Science: Fundamentals & Investigations, Chapter 7 8
The Function The Function and Structure of DNA and Structure of DNA
o Nitrogenous Bases—pairs of molecules that form the rungs of the DNA “ladder”
o Four types of Bases• A (adenine)• C (cytosine)• G (guanine) • T (thymine)
The Function The Function and Structure of DNA and Structure of DNA
o Base-Pairing Rules• adenine (A) binds only with thymine(T)• cytosine (C) binds only with guanine (G)
How DNA is inheritedHow DNA is inherited
o ½ (23 chromosomes) from each parent
o This results in one allele (form of a gene) from each parent
GenomeGenome
o Total amount of DNA in each cello Each cell contains all the DNA but only some
is used – allowing very different types of cells/tissues
o Portions of DNA that are used are called exons. Unused portions (non-coding DNA) are called introns.
o This is VERY important for DNA fingerprinting.
DNA Identification DNA Identification
o Most DNA is the same in all humans but some variation exists allowing for identification
o Polymorphisms: Non-coded DNA that contain unique patterns of repeated base sequences that that are unique to individuals
o DNA Fingerprinting (Profiling) isolates and analyzes polymorphisms
o DNA fingerprints appear as a pattern of bands on X-ray film.
DNA Profile DNA Profile
Due to unique polymorphisms each person will show a unique pattern!
Because they are unique they are called DNA fingerprints
DNA Profile DNA Profile
Two types of repeating DNA sequenceso 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)
o 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…)
DNA Profile DNA Profile
o STR’s are much shorter than VNTR’s and are becoming the preferred method of analysis
o VNTR and STR data are analyzed for • tissue matching• inheritance matching
o Tissue Matching• Two samples that have the same band pattern are from the
same person
o Inheritance Matching• Each band in a child’s DNA fingerprint must be present in at
least one parent
DNA Profile - paternity testDNA Profile - paternity test
DNA Profile - paternity testDNA Profile - paternity test
Who is the father of Kid 1?Kid 2?How did you know?
DNA Profile – tissue match DNA Profile – tissue match (crime scene)(crime scene)
DNA Profile – tissue match DNA Profile – tissue match (crime scene)(crime scene)
Which suspect is guilty? Why did they have the boyfriend give a sample? They female cells?
DNA Profile – tissue match DNA Profile – tissue match (crime scene)(crime scene)
DNA Population Databases DNA Population Databases
o 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
o Examples• Identifying the suspect in a crime • Identifying an alleged father in a paternity case
Sources of DNA Sources of DNA
o Biological evidence: examples include saliva, blood, skin, hair, seminal fluid
o Individual evidence is capable of identifying a specific person.
o Small amounts may be only trace evidence – but a little bit of DNA can be copied to make a larger testable amount
o Polymerase chain reaction (PCR) technique generates multiple copies of DNA evidence
Collection and Collection and Preservation of DNA Preservation of DNA
1. Use disposable gloves and collection instruments
2. Avoid physical contact, talking, sneezing, and coughing in the evidence area
3. Air-dry evidence and put it into new paper bags or envelopes
4. Dry or freeze the evidence
5. Keep evidence cool and dry during transportation and storage
Preparing DNA Samples Preparing DNA Samples for Fingerprinting for Fingerprinting
Extraction1. Cells are isolated from biological evidence such
as blood, saliva, urine, semen, and hair
2. The cells are disrupted to release the DNA from proteins and other cell components
3. The DNA can be extracted from the cell nucleus
Preparing DNA Samples Preparing DNA Samples for Fingerprinting for Fingerprinting
Amplification o VNTR analyses—polymerase chain reaction
(PCR) can be used to amplify the DNA that contains the VNTRs
o STR profiles—restriction enzymes are unnecessary; PCR allows the amplification of the strands with STR sequences
PCR – DNA copy machinePCR – DNA copy machine
o http://www.youtube.com/watch?v=2KoLnIwoZKU
Preparing DNA Samples Preparing DNA Samples for Fingerprinting for Fingerprinting
1. DNA is mixed with special proteins called restriction enzymes.
2. 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
Electrophoresis Overview
Forensic Science: Fundamentals & Investigations, Chapter 7 29
Preparing DNA Samples Preparing DNA Samples for Fingerprinting for Fingerprinting
Electrophoresis o DNA samples are placed in gels through which
electronic currents are passed
o DNA fragments line up in bands along the length of each gel
Electrophoresis Electrophoresis
o An electrophoresis apparatus running five sample of DNA
o Arrows show the movement of the negatively charged DNA fragments through the gel matrix
Probes Probes
o Humans have A LOT of DNAo To limit what we are looking at DNA probes are usedo 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)o In most criminal cases, 6 to 8 probes are used
Analysis of DNA Analysis of DNA Fingerprints and Applications Fingerprints and Applications
o 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
Southern Blot/Probes Clarification
Humans could have 100’s of thousands!!
6 – 8 probes (sequences) are used for crime scene analysis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . SummarySummary . . . . . . . .
o DNA contains the information needed for replication in a sequence of nitrogenous bases.
o DNA analysis allows even a small sample of tissue to be identified with a single individual.
o DNA contains, in non-coding regions called junk DNA, many repeated sequences that vary in number between individuals.
o These differences between individuals can be used to produce a DNA fingerprint for an individual.
. . . . . . . . . . . . . . . . . Summary. . . . . . . . . . . . . . . . . Summary
o Polymerase chain reaction (PCR) for DNA amplification has largely eliminated the problem resulting from the tiny samples usually available.
o DNA evidence must be collected carefully to avoid contamination with other DNA.
o DNA analysis involves extraction, electrophoresis, and visualization.
o DNA profiles are kept by police agencies in electronic databases.
Gel Electrophoresis of Food Coloring - LAB
o You must wear goggles at all timeso Be patient and take turns with micropipetteso Follow all directionso Be aware that we are using electricity to
separate colors – be cautious
Centrifuge
o Place all samples into centrifuge and turn on for about 10 seconds
o All your liquid should be at the bottom of your tube
How to Use a micropipette
Eject tips into beaker – use a new tip for each color!
Use the first stop to “suck up” sample, and second stop when inserting in gel!
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
o Carefully slide cover onto chamber, make sure unit is turned OFF and plug in black to black – red to red
o Turn on and make sure voltage is at 110V – watch your gel “run”
DNA Detectives Lab
DNA Detectives – Day 1
o Read procedure and be prepared to work on questions for tomorrow.
o Part I will be completed for you – We will begin with Part II (Method 2: Submarine)
o We will load and “run” gels today. o Make a Ziploc bag with your names on - so
that gel can be saved for staining tomorrow!
