DNA fingerprinting webquest

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?

yes i do because the writers of the stores were trying to get the dr. convicted because they were putting lies in the stories they wrote.

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 restriction enzymes work like scissors cutting the long dna molecules at diffrent locations

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

it will act like a molecular strainer 

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

because it hard to pick up the jell so the dna is trnsfred the the nylon membrane so it is easy to pick up and work with

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

it indicates were the DNA mixture is

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?

a photo , a police identification line up and, a flashlight similar to the one at the crime and the rubber of his shoes.

7. What did the DNA evidence show?

the DNA evidence showed the it was the man who emited to the crime

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

it could because it would go throw the database of dnas and find the right match.

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

25% of people ar unjustly convicted of sexual assault cases.

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?

 is it highlights on the one hand the tremendous potential of this technology that it is a science that can be the equivalent of the videotape of the commission of the crime. Yet, on the other hand, it points out that this is not a law of science that we're dealing with, such physics such as the law of gravity.

Instead, we're talking about an applied science, an applied technology and whenever people get involved in the application of science is much opportunity for mistake, error and for much worse. And so we have to be very rigorous in the kinds controls that we exert when we utilize this tremendously powerful new technology to make sure that it's used wisely and cautiously.