Welcome back! Take out your notes from chapter 7: DNA

Fingerprinting Analysis

Watson & Crick• Discovered the basic shape of

DNA

• Won the Nobel Prize in 1953 for this discovery

From studies of DNA we have found----

No two people have identical DNA except..

Identical TwinsAnd they can be identified separately by other means

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

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.

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

DNA analysis requires

• Obtaining a sample for analysis

• Extract DNA and amplify it (PCR)

• Cut the sample with digestive enzymes called restriction endonucleases

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.

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.

• Place the cut DNA in an electrophoresis chamber and conduct a separation

• Compare the results of the separation to samples from various suspects

Running a Gel

Gel Electrophoresis

http://www.lewport.wnyric.org/jwanamaker/animations/Chrom&Elpho.html

Click on me, them click menuThen ‘view the process of electrophoresis’

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

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

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?

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.

Who was at the crime scene?

A real DNA profile

Another ‘tagged’

Lane 1 crime sceneLane 2 Suspect #1Lane 3 ControlLane 4 standard Lane 5 Suspect #2Lane 6 ControlSuspect #1 or #2?

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.

                

               

                 

                

                

       

                                                                  

            

    

           

                                

    

  

          

                                

Internet Search

• Have any persons previously found guilty be proven innocent by DNA testing?

• Research ‘The Blooding’

• Research ‘The Fugitive’

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?

Gattaca

• Please respond to the scene and implications