miniPCR bio™ Electrophoresis Forensics Lab. Wrongfully Convicted? Instructor's and Student's Guide
Version: 1.1 - Release February 2022 - © 2022 by miniPCR bio™
Student's Guide
P./9
Background and significance
Forensic DNA analysis
-
DNA analysis is considered the gold standard in forensic science. But why is this the case? When
comparing two people's DNA, more than 99% will be identical. Even with so much similarity, there
are more than enough differences to make every person's genetic sequence unique. This makes DNA
analysis a powerful tool for identification of individuals. Scientists can isolate DNA from biological
crime scene evidence, like a bloodstain or a hair follicle, and use the information in the DNA to match
the sample to a specific person.
As forensic approaches have evolved, there have been several methods for matching DNA evidence
to individuals. Most forensic DNA analysis looks at regions of the genome that vary in length
between individuals.
Short tandem repeats
-
Most modern forensic DNA analysis focuses on short tandem repeats (STRs). STRs are short
sequences, typically 2 to 5 DNA bases, that repeat several times in a row (Figure 1). The number
of times the bases repeat, however, varies between people. Therefore, the length of DNA where
Figure 1. Short tandem repeats
STRs are short DNA sequences that repeat several times in a row. For
example, STR 1 is a specific location in the human genome where the
sequence GATA is repeated between 5 and 16 times.
the STRs are located also varies
between people. Forensic scientists
take advantage of this and measure
these differences in length to
compare DNA between individuals.
There are many locations in
the human genome where the
number of copies of a specific STR
varies between people. Forensics
scientists give each STR a complex
name that reflects its location in
the genome, but for simplicity, we
will refer to an example as STR 1. At
this location in the human genome,
the sequence GATA is repeated
anywhere between 5 and 16 times
(Figure 1).
STR 1
...... GATA GATA GATA GATA GATA ......
...... GATA GATA GATA GATA GATA GATA ......
5 REPEATS
6 REPEATS
...... GATA GATA GATA GATA GATA GATA GATA ......
7 REPEATS
UP TO 16 REPEATS
