DNA Fingerprinting Exercise:

1
DNA Fingerprinting Exercise Blood found at a
murder scene is thought to be that of the
attacker (there was a vicious fight and the
attacker did not got away unscathed!). We have
three suspects. Carry out a DNA fingerprint on
blood samples from each suspect and on blood
found at the scene. We are going to use
restriction endonucleases and for simplicity we
will only test two loci (we arent really
bothered about catching the real murderer, just
so long as we get a conviction!). Solve the
crime! 1. Restrict each DNA sample with the
following restriction endonucleases ECORI
GAATTC and Hind III AAGCTT CTT
AAG TTCGAA And calculate the
fragment sizes in bp. Suspect one has been done
for you already
29 bp fragment
-GGCTACTGGAAGCTTAATGTCGGTCGGTCGGTCGGTCGTTCGAATTGCA
TGGGCG- -CCGATGACCTTCCAATTACAGCCAGCCAGCCAGCCAGCAAG
CTTAACGTACCCGC-
-GGCTATGGAATTCGGGTATAGTATAGTATAGCCAAGCTTGCTATTGCCC
TGAGGCC- -CCGATACCTTAAGC CCATATCATATCATATCGG
TTCGAACGATAACGGGACTCCGG-
26 bp fragment
Suspect 2
-CTGGAAGCTTGGCCGGCCGGCCGGCCGGCCGGCCGGCCGGCCGGCCTTC
GAAT- -GACCTTCGAACCGGCCGGCCGGCCGGCCGGCCGGCCGGCCGGC
CGGAAGCTTA-
-TTGAATTCATCGATTAATTAATTACCAAGCTTGCTATTGCCC
TGAGGCCGCTATGCT- -AACTTAAGTAGCTAATTAATTAATGGTTCGAA
CGATAACGGGACTCCGGCGATACGA-
Suspect 3
-ATTGATTGATGGCTACTGGAAGCTTAACTAACTAACTGCTTCGAATTGC
ATCGGCG- -TAACTAACTACCGATGACCTTCGAATTGATTGATTGACGA
AGCTTAACGTAGCCGC-
-TACCTTAAGCATACATACATACATACATACATACATACATACATACATA
CAATTCGAA- -ATGGAATTCGTATGTATGTATGTATGTATGTATGTATG
TATGTATGTATGTTAAGCTT-
2
2. Plot the position the fragments would take on
the following electrophoretic gel. The blood
found at the scene has already been done for you
3. Which suspect do you think committed the
murder?

• Uses of DNA fingerprinting
• To test whether or not parents carry a
  disease-causing mutation that may be passed on to
  their offspring, e.g. sickle-cell disease, cystic
  fibrosis.
• To determine the real father of a child (paternal
  testing).
• To test crime suspects to see if their DNA
  matches that found at the crime scene.
• Problems with DNA fingerprinting
• False Negatives mistakenly declaring that there
  is no match.
• False Positives mistakenly declaring that there
  is a match. Is this an acceptable error?
• Although the probability of two people
  coincidentally having matching DNA fingerprints
  is extremely small, the process of obtaining a
  DNA fingerprint by gel electrophoresis is prone
  to experimental error. The same DNA sample will
  never give two identical gels!