miniPCR bio™ Electrophoresis Forensics Lab. Wrongfully Convicted? Instructor's and Student's Guide
Version: 1.1 - Release February 2022 - © 2022 by miniPCR bio™
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Instructor's Guide
Notes on lab design
This lab serves as an introduction to forensic DNA analysis. While many forensic labs focus on
using DNA to convict someone of a crime, we believe it is equally important to consider how DNA
evidence can exonerate someone who was wrongly convicted. While the scenario presented in
this lab is fictional, it is inspired by real cases where people have been wrongly convicted and later
proven innocent through post-conviction DNA analysis.
This lab introduces the examination of short tandem repeats to generate DNA profiles. We believe
our approach provides the right balance between intellectual engagement, inquiry, and accessibility.
The design of this lab has simplified certain elements to achieve these goals.
• This lab uses prepared DNA to simulate the results of PCR amplification of STRs from DNA
evidence.
• While forensic STR analysis typically examines at least 20 STR loci, this lab examines only one
to allow for clear interpretation of the results.
• Forensic scientists use capillary electrophoresis to separate STR DNA fragments, but this
technique requires expensive and specialized equipment. We substitute gel electrophoresis,
which separates DNA fragments using the same principles as capillary electrophoresis.
• To allow for clear resolution of STR alleles by gel electrophoresis, the range of DNA fragments
used is greater than what is observed for a given STR locus. Most STR loci have a four
nucleotide repeat sequence and around 10 alleles. This means the size difference between
the smallest allele and the largest allele is typically only around 40 bases. We have used size
differences in the hundreds of bases as these are easily resolvable on an agarose gel.
Before carrying out this lab, students should have basic competence using a micropipette, and
should understand the concept of gel electrophoresis. See the Additional Student Supports section
of this lab for ways to scaffold this assignment for students who may be less comfortable with the
aforementioned skills.
