DNA Detective Work

DNA DETECTIVE WORK

Unless you have a twin, no one in the world has a DNA sequence identical to yours. Although 99 percent of the DNA is the same in all humans, certain segments vary widely. Differences in these segments are detected through DNA fingerprinting. A small amount of tissue, such as blood, hair, or semen, is all that is needed to create a DNA fingerprint. The sample is cut up using enzymes and the segments are separated by size through gel electrophoresis. DNA is made visible either with radioactive probes or by staining. This reveals a pattern of bars: the DNA fingerprint. If the two DNA fingerprints match, they probably came from the same person. If they don't match, they certainly came from different individuals. In recent years, a number of people convicted of crimes have been exonerated based on DNA evidence.

Activity

In this exercise, you will learn the basics of DNA fingerprinting and consider the use of DNA in criminal investigations.

Part 1.

Use your browser to go to NOVA’s web site about “Killers Trail,”  the story behind the man who inspired the Fugitive TV series and later the movie version starring Harrison Ford:

http://www.pbs.org/wgbh/nova/sheppard/

Click on the “Chronology of a Murder” section and read about the events that led up to the murder trial of Dr. Sam Sheppard.

1. In your opinion, what role (if any) did newspaper stories and editorials have in the outcome of the original trial of Dr. Sam Sheppard?

So in my opinion, they have a huge a effect because the people believed what was put in the newspaper even if it wasn't true.

Go back to the Killers Trail homepage and select ”Create a DNA Fingerprint.”

Read about the crime and the suspects then go on to part 2. Answer the following questions about the technique as you go through the simulation:

2. What is the function of the restriction enzymes in DNA fingerprinting?

The function of the restriction enzymes in DNA fingerprinting, they work similar to scissors that cut across long DNA molecules at different locations.

3. What is the function of  the agarose gel electrophoresis step?

The function of the agarose gel electrophoresis step is that its a gel jell-o like substance that will act like a molecule strainer that allows tinier pieces of DNA to move through more easier than larger pieces.

4. Why is a nylon membrane used to blot the DNA?

Nylon membrane is used to blot the DNA because DNA transfers to the nylon.

5. What does a dark spot on the X-ray film indicate?

A dark spot on the x-ray film indicates the radioactivity from the probes.

Part 2.

Use your browser to go to Frontline's "What Jennifer Saw" at

http://www.pbs.org/wgbh/pages/frontline/shows/dna/.

The material on this site is about a man convicted of rape but later exonerated by DNA evidence. To read a summary of the case, choose the link to Ronald Cotton's wrongful conviction, then choose "Summary of Cotton's Case."

In the interviews section, read the interviews with DNA expert Peter Neufeld and lawyer Barry Scheck.

Answer the following questions:

6. What evidence was initially used to convict Cotton?

The evidence that was initially used to convict cotton was a flashlight that resembled the one used by the assailant and the rubber of the tennis shoes which was consistent with the rubber found at one of the crime scenes.

7. What did the DNA evidence show?

The DNA evidence showed no match to cotton. The results matched a convicted felon who had confessed to a crime earlier.

8. How could DNA fingerprinting be used to prevent a false conviction if a case like this was being tried today?

The DNA fingerprinting could be used to convict false convictions today by getting the correct results from evidence found on the crime scenes and match to the correct DNA from the convict.

9. What percentage of convicts are unjustly convicted of sexual assault cases, according to Neufeld and Scheck?

The percentage of convicts that are unjustly convicted of sexual assault cases is 15 percent.

10. The O.J. Simpson trial was one of the most visible trials that attempted to use DNA evidence.  In the end, the DNA evidence was not satisfying to the jury, who acquitted Simpson.  What do Neufeld and Scheck believe about the impact of the O.J. Simpson trial on the use of DNA evidence?

Neufeld and Scheck believed that the case had a lot of potential from when it had first started. Neufeld said they have to be very rigorous in the kinds controls that they exert when they utilize this tremendously powerful new technology to make sure that it's used wisely and cautiously. So the OJ trial had a big impact they believe from where DNA evidence started.