miniPCR bio™ Electrophoresis Forensics Lab. Wrongfully Convicted? Instructor's and Student's Guide
Version: 1.1 - Release February 2022 - © 2022 by miniPCR bio™
P./34
Instructor's Guide
Expected results
Gel electrophoresis results are expected to resemble the gel image below.
• Victim DNA: should contain 2 DNA fragments - 250 bp and 150 bp
• J.M. DNA: should contain 1 DNA fragment - 400 bp
• DNA evidence 1: should contain 2 DNA fragments - 700 bp and 250 bp
• DNA evidence 2: should contain 2 DNA fragments - 250 bp and 150 bp
Interpretation
• J.M.'s DNA does not match either evidence sample. Even though only one STR was analyzed,
J.M. can definitively be excluded as the source of the DNA evidence collected from the crime
scene.
• The victim's DNA matches DNA evidence 2. This suggests that the second evidence sample
may have come from the victim. It is not uncommon for there to be ample victim DNA after
a violent crime. To be more confident of this hypothesis, more STR loci would need to be
examined to generate a comprehensive STR profile.
• DNA evidence 1 represents an unknown individual since neither the victim nor J.M. has a 700
bp STR fragment. A reasonable next step in the investigation would be to search for a suspect
that matches this DNA sample. If more STR loci were examined to generate a complete
evidence STR profile, then a CODIS database search could be performed.
Base
Pairs
1200
700
500
300
200
100
Ladder
Victim
DNA
J.M.
DNA
DNA
Evidence
1
DNA
Evidence
2
