DNA as Evidence

Julie A. Ellsworth

Truckee Meadows Community College

DNA evidence entered the courtroom for the first time in 1985, and is now
commonly submitted as evidence to try to prove guilt or innocence. At least 100 people
have been exonerated using DNA testing and 10 of those people have been freed from
death row. In this module students will be presented with a basic introduction to DNA and how it can
be used as evidence in forensic investigations or identity disputes. They will answer
questions to clarify their understanding and calculate the probability of a perfect DNA
profile match for two datasets. Understanding the power of DNA evidence requires
understanding the multiplication rule of probability. As more pieces of a person’s DNA
are analyzed, the probability that the resulting DNA profile will perfectly match another
person becomes smaller and smaller.

The mathematics is use of percentages and proportions; understanding and applying the
multiplication rule of probability.