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:
Click on the “Chronology of a Murder” section and read about the events that led up to the murder trial of Dr. Sam Sheppard.
- In your opinion, what role (if any) did newspaper stories and editorials have in the outcome of the original trial of Dr. Sam Sheppard?
In my opinion I think that some people are stretching the truth about this and they are leaving facts out because they think he is guilty. But then there are some people that are thinking that Marilyn Sheppard needs justice and who is going to speak for her. It did say that on July 1989 Richard Eberling, an interior decorator and the former window washer at the Sheppard home, is convicted of aggravated murder in the death of Ethel May Durkin. But at the beginning it says that window washing company employee Vern Lund leaves town. Both guys are window washers at the Sheppards home and one guy had be convicted of murder and when they found Marilyn dead the other man left too.
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:
- What is the function of the restriction enzymes in DNA fingerprinting?
A-It cuts along different locations. The lengths of the fragments will vary from person to person because the code for every person’s DNA is different. Some of the fragments will be long, others will be short.
- What is the function of the agarose gel electrophoresis step?
A-The agarose gel is thick, porous, Jell-O-like substance. It will act as a molecular strainer, allowing smaller pieces of DNA to move through more easily than larger pieces.
- Why is a nylon membrane used to blot the DNA?
A-You do that because you just added probes to the nylon membrane, and what they do is attach themselves to DNA fragments on the nylon membrane.
- What does a dark spot on the X-ray film indicate?
A-The probes are now present at only a few locations on the membrane, exposing corresponding areas on the X-ray film.
Part 2.
Use your browser to go to Frontline's "What Jennifer Saw" at
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:
- What evidence was initially used to convict Cotton?
A-A photo identification was made by one of the victims, then a police lineup identification wa made by one of the victims. A flashlight in Cotton’s home resembles the one used by the assailant. Then the rubber from Cotton’s tennis shoe was consistent with rubber found at one of the crime scenes.
- What did the DNA evidence show?A-The DNA evidence shows that the samples from one victim were too deteriorated to e conclusive, but the samples from the other victim’s vagainal swab and underwear were submitted to PCR testing and showed no match to Cotton.
- How could DNA fingerprinting be used to prevent a false conviction if a case like this was being tried today?A- DNA fingerprinting can be used to prevent a false conviction by the fact that there is a poor innocent person dropped their gloves on the floor and a criminal picks them up and commits a crime in those gloves then there is more of a chance of the criminal getting away with it because it would have the poor innocent persons DNA.
- What percentage of convicts are unjustly convicted of sexual assault cases?A- 28%
- 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?A- They review cases of people who say that they have been falsely convicted and arrange for DNA test that may claim of innocence.
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