Welcome back! Take out your notes from chapter 7: DNA Fingerprinting Analysis.
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Transcript of Welcome back! Take out your notes from chapter 7: DNA Fingerprinting Analysis.
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Welcome back! Take out your notes from chapter 7: DNA
Fingerprinting Analysis
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Watson & Crick• Discovered the basic shape of
DNA
• Won the Nobel Prize in 1953 for this discovery
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From studies of DNA we have found----
No two people have identical DNA except..
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Identical TwinsAnd they can be identified separately by other means
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DNA Fingerprinting Analysis
• Can be used to match a suspect to a crime scene with a high degree of probability
• Can be done on semen, saliva and blood
• Can be performed on body cells
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Sources of DNA • A perpetrator may leave biological evidence, such
as saliva or blood, at a crime scene. • This individual evidence is capable of identifying
a specific person. • But a small amount of biological evidence might
be considered only trace evidence, and it may be consumed during forensic testing.
• In 1993, however, the polymerase chain reaction (PCR) technique was invented. It generates multiple copies of DNA evidence.
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Minute amounts of DNA
Can be amplified by PCR. This process allows the DNA to be copied many times so that a large enough sample is available for analysis
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DNA analysis requires
• Obtaining a sample for analysis
• Extract DNA and amplify it (PCR)
• Cut the sample with digestive enzymes called restriction endonucleases
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DNA Identification
The number of copies of the same repeated base sequence in DNA varies among individuals.
Variable Number of Tandem Repeats (VNTR)
• Within junk DNA, sequences of DNA are repeated multiple times.
• Some can be 9-80 bases in length.
Short Tandem Repeats (STR) • Within junk DNA, other sequences of DNA also are repeated
multiple times. • These usually are only 2-5 bases in length and are becoming
the preferred sequences for analysis.
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DNA Profiling and DNA Population Databases
• VNTR and STR data are analyzed for (a) tissue matching and (b) inheritance matching.
• Population genetics is the study of variation in genes among groups of individuals.
• Calculations can be made based on these groups to determine the probability a random person would have the same alternative form of a gene (an allele) as (a) a suspect in a crime or (b) an alleged father in a paternity case.
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• Place the cut DNA in an electrophoresis chamber and conduct a separation
• Compare the results of the separation to samples from various suspects
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Running a Gel
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Gel Electrophoresis
http://www.lewport.wnyric.org/jwanamaker/animations/Chrom&Elpho.html
Click on me, them click menuThen ‘view the process of electrophoresis’
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How to cut DNAhttp://www.lewport.wnyric.org/jwanamaker/animations/Chrom&Elpho.html
Click on me, them click menuThen ‘view how to cut DNA for gel electrophoresis’ and follow directions
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How to sort DNA by size
http://www.lewport.wnyric.org/jwanamaker/animations/Chrom&Elpho.html
Click on me, them click menuThen ‘explanation of how molecules can be sorted using a gel’.. and follow directions
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Run a gel
• Compare the results and determine whether the suspect was linked to the victim and crime scene.
• Tagged samples are the evaluated. The tagging is done using a radioactive ‘probe’ which binds to specific sequences on DNA
What do your results indicate?
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Probes
• DNA probes are used to identify the unique sequences in a person’s DNA.
• Different DNA probes are made up of different synthetic sequences of DNA bases compli-mentary to the DNA strand.
• The probe binds to complimentary bases in the strand (see the fragmentary DNA bands above).
• In most criminal cases, 6-8 probes are used.
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Who was at the crime scene?
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A real DNA profile
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Another ‘tagged’
Lane 1 crime sceneLane 2 Suspect #1Lane 3 ControlLane 4 standard Lane 5 Suspect #2Lane 6 ControlSuspect #1 or #2?
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Analysis of DNA
Fingerprints
and Applications
• Bands and widths are significant in matching samples of DNA.
• DNA fingerprinting can (a) match crime scene DNA with a suspect, (b) determine maternity, paternity, or match to another relative, (c) eliminate a suspect, (d) free a falsely imprisoned individual, and (e) identify human remains.
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Internet Search
• Have any persons previously found guilty be proven innocent by DNA testing?
• Research ‘The Blooding’
• Research ‘The Fugitive’
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Discussion in groups of 4
• A. Should the government be able to have access to everyone’s DNA? Explain your point of view.
• B. Should the DNA of relatives of convicted criminals be available?
• C. Should we screen everyone’s DNA at birth to identify possible health issues?
• D. Should we be allowed to genetically alter plants and animals to make food more desirable for humans?
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Gattaca
• Please respond to the scene and implications