DNA Fingerprinting
0 Is a technique used by forensic scientists to identify
people based on their DNA profiles
0 The key to DNA fingerprinting is Restriction Fragment
Length Polymorphisms (RFLPs)
When is it used?
0 Crime Investigations
0 Rape
0 Violent Crimes
0 Familial Relationships
0 Paternity tests
How Specific Are RFLPs?
0 Under normal circumstances, no other human has
your exact complement of genes, unless…
0 You are an identical twin
Murder Case
After going missing, Lynda Mann, a 15-year old
schoolgirl was raped and murdered in the grounds of
Carlton Hayes psychiatric hospital in Narborough,
Leicestershire, in November 1983. Forensic
examination of semen sample that it was a type found
only in 10% of men, and was from someone with type A
blood. However, the police did not find a suspect. In
1986, another 150year old schoolgirl, Dawn Ashworth,
was similarly sexually assaulted and strangled in the
nearby village of Enderby, and semen samples showed
the same blood type.
Suspect 1
0 Richard Buckland (17 years old)
0 Local with learning disabilities
0 Worked at Carlton Hayes psychiatric hospital
0 Seen near murder scene of Dawn Ashworth
0 Knew detailed information regarding body of deceased
0 Confessed to the murder of Dawn Ashworth but not to
the murder of Lynda Mann
Suspect 2
0 Colin Pitchfork (27 years old)
0 Local baker
0 Previous convictions for flashing
0 Paid someone to give a false semen sample to police
during the investigation supposedly because of his prior
convections.
Steps
1.
2.
3.
4.
5.
6.
7.
Extract DNA
Amplify DNA
Cut DNA
Sort DNA
Denature DNA
Hybridize DNA
Make an X-Ray
Extract DNA
0 We performed an extraction last week using cold
ethanol. Keep in mind that there are other ways to
extract DNA.
0 We will be going through these steps using the DNA
sheet that you should have printed out.
0 If you do not have the sheet, I have a few extras.
Amplify DNA
0 We amplify DNA using Polymerase Chain Reaction
(PCR).
0 This allows us to increase the total amount of DNA
that we have
0 For our exercise, everyone having their copy of DNA
will act as the amplification
Cut DNA
0 To cut DNA, Restriction enzymes are used.
0 These enzymes cut DNA by recognizing specific sites in
chains of DNA
0 We will act as restriction enzymes and cut our DNA at the
indicated sites.
0 Make sure that the sites match exactly
NeoSci 1
5’ GG|CC 3’
3’ CC|GG 5’
NeoSci 2
5’ GA|AG 3’
3’ CT|TC 5’
Sort DNA
0 After the DNA is cut using restriction enzymes, it must
be sorted using gel electrophoresis
0 This process separates DNA fragments based on size
0 We will cut paper DNA fragments out ant place them
on our paper gel
0 Fill out p. 215 by placing dark lines at any location
where a fragment would be present
Denature DNA
0 After the DNA has been sorted, it must then be
denatured using either heat or chemical.
0 To denature our DNA, we will remove the yellow
strips from the bottom of the fragments in our lanes
Hybridize DNA
0 This step binds a radioactive probe to the fragmented
DNA so that it can be seen.
0 We will cut out the “T C C” probes and place them
under fragments with the corresponding letters “A G G”
Make an X-Ray
0 The process of taking an X-Ray of hybridized DNA is
called Autoradiography
0 Fill in lines on p. 214 to indicate fragments where
hybridization has occurred.
Results
0 Suspect 2: Colin Pitchfork is the murder.
0 Colin Pitchfork was the first person ever to convicted
of murder based on DNA fingerprinting evidence.
Before you leave lab
0 Clean up your work station
Before next lab
0 Read Lab 7 – The Cardiovascular System
0 Do Online Prelab
0 Complete sections in lab manual for lab notebook
check