Weekly Online Lesson Online Lesson Archive Grade Level: 9-12 Subject: Biology/Law

DNA Evidence

In Boise, Idaho, a man who has spent 17 years on death row has been released from prison after a new type of DNA testing showed reasonable doubt about his guilt in the 1982 murder of 9-year-old girl. Charles Fain, the defendant, has maintained his innocence throughout his incarceration.

Fain was released on August 42, 2001, when prosecutors declined to pursue a new trial.

Fain's guilt in the original trial was largely based on an FBI forensics expert's testimony that hairs found on the victim's body may have been Fain's. But recent breakthroughs in DNA identification led a forensic laboratory to conclude in June that the hairs were not his.

Scientists typically study DNA by performing tests on the nucleus of human cells. But human hair has presented a problem because the cells do not contain a nucleus. Fain's case was among the first in the nation in which scientists used mitochondrial DNA, which is found in hair, to help determine its human origin.

In this week's lesson, you will learn about DNA testing and its application in modern forensic criminology.

Dolan DNA Learning Center

If you're not quite sure what DNA is, the place to start this week's lesson is definitely the Dolan DNA Learning Center. Start by clicking DNA from the Beginning on the right, and then click Enter. This special resource section is an extensive tutorial about genetics, inherited traits, and DNA. It's hard to say where you should begin; the site features 41 concepts. Start with the first concept, which is called Children resemble their parents. Read the introduction to the concept. If you understand it already, move on to the next. When you start to find that you are unfamiliar with a concept, dig a little deeper using the links at the bottom of the page: Animation, Gallery, Audio/Video, Bio, and Problem. You will start learning about the DNA connection around Concept 15.

It may take you some time to get through this genetics primer. When you're ready, return to the homepage, click Features, and then click DNA Fingerprinting at the bottom of the page. Read the introduction, which explains what DNA evidence is all about. Below the intro is a link to a Shockwave animation called DNA Detective, where you can learn the process of DNA identification in greater detail. Click How to Make a DNA Fingerprint and work through the presentation. According to the animations, what is used to cut up DNA into a precise set of fragments? How are the fragments separated by size? How are the sorted fragments applied to a nylon membrane?

The next links in the animation show how DNA evidence was applied in a criminal case, a paternity case, and a case involving a thoroughbred horse. Investigate each of these cases as you please (note that you may find the criminal case somewhat disturbing).

Why Files

Return now to the DNA Fingerprinting page. At the bottom you will find a list of Internet links; click How scientists and forensic experts use technology to analyze evidence from crime scenes from the University of Wisconsin's Why Files. This site is all about forensic science (not just DNA evidence), and it's written in a light, conversational way (fun reading, gruesome topic). Read the first page, and then click the smoking gun (more) at the bottom of every page to continue. Or, of you'd rather skip right to the DNA chase, click DNA identification and start from there. How accurate can DNA evidence be? What are some of the problems with DNA fingerprinting?

How DNA Evidence Works

One last place to visit on this exploration of DNA evidence is Marshall Brain's HowStuffWorks site, and the article How DNA Evidence Works. Again, read the introduction, and then click Next Page at the bottom to move on (or use the navigation on the right side of the page).

Is DNA evidence better for establishing guilt or innocence? What are length polymorphisms and how do they relate to DNA evidence? What's wrong with DNA fingerprinting if it involves an identical twin? How does math come into play with regards to DNA evidence?

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