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 “Killer’s 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/

  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?

i think it had a big impact on the trial because the people believed the newspapers that were lying to them.

Go back to the Killer’s 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:

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

They act like scissors and cut the molecule in certain places

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

act like a strainer allowing dna to move through larger pieces

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

because its very hard pick up so when you put the nylon on it, it gets soaked up

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

Indicating where the probes attach themselves to the DNA

 

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:

  1. What evidence was initially used to convict Cotton?

The flashlight that they found at Cotton’s home was the same one they thought seemed like the murder weapon and also the rubber found at the crime scene was consistent with some found at his house.  He was also identified during investigation line up. Also he was identified by a photo.

  1. What did the DNA evidence show?

It shows that there was a very high number of people convicted by the jury due to evidence.  It also shows that the suspect was sometimes innocent and the evidence helps to show that,  but the justice system sometimes has cracks that they fall through and end up being found guilty.

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

It would be asked for as backup evidence for proof that there was a false conviction.  If they were guilty, it would be used against them to prove them as guilty.

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

According to Neufeld and Schek around 25% of convicts are unjustly convicted of sexual assault cases.

 

  1. 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?

They would believe that he was unjustly acquitted and that the DNA evidence should have held more sufficient clause.