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?

1.     In my opinion the rle of newspaper stories and editorials played a major part in the outcome of the original trail of Dr. Sam Sheppard. Because of the pressure the police and jury felt from the attacks from the media, they unlawful arrested Sheppard just to please them. The media complained or questioned something they did what they could to please them. Even if it ment putting an innocent man in jail with out a proper trial.

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?

1.     The restriction enzymes work like scissors to cut the long DNA molecules at different locations. Where the enzymes ut depends on the code within the DNA molecule and the code within the enzymes.

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

1.     Acts as a molecular strainer, allowing smaller pieces of DNA to move through more easily than larger pieces.

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

1.     The DNA is sucked into the membrane as liquid traveled up from the gel toward an absorbent material that was placedover the membrane.

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

1.     Your fingerprint

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?

1.     A photo identification was made by one of the victims.

2.     A police lineup identification was made by one of the victims.

3.     A flashlight in Cotton's home resembled the one used by the assailant.

4.     Rubber from Cotton's tennis shoe was consistent with rubber found at one of the crime scenes.

7.                 What did the DNA evidence show?

1.     That Cotton was not the rapest and that another inmate in prison for similar crimes had committed the rapes. He ven addmitted it to another inmate but the superior court refused to alow known to the jury.

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

1.     DNA fingerprinting gives us hardcore edvidence on weather or not someone committed. This way those who are innocent won’t be put way for something they didn’t do.

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

1.     25%

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?

1.     They talked about how though DNA helps in keeping innocents from being wrongflly convicted they can still be wrong, but it depends on if the person working on it makes a mistake.