As we learn more about DNA, we should apply these concepts to practices used in current sciences. One field that works with DNA on a daily basis is forensic science. Even though 99% of human DNA is the same, the 1% difference causes each person's DNA to be unique, except for that of unusual births, such as twins. By testing tissue samples with gel electrophoresis, a person's DNA code could be discovered, and if the results matched to another set of DNA, then the specific person could be identified. This is applies to forensic investigations in that if DNA is found at a crime scene, it can be matched to a suspect. Since the discovery of DNA technology, multiple people convicted of crime have been exonerated based on DNA evidence. Since this is such an interesting application of science, we are going to explore this topic more through an activity using this source.
To begin with, we are going to read about and analyze the events surrounding the murder trail 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?
As I read through the chronicle of events, it became clear to e that media and press coverage played a significant role in this case. A majority of the headlines presented a very biased stance on the trial, pressuring officials to take action. It is usual for this to occur in a murder investigation, but not to this extent. This coverage also caused the jury to have a bias toward the case; there were multiple occasions in which a juror questioned the judge on a topic that had only been discussed in the media, which proved to be false.
2. What is the function of the restriction enzymes in DNA fingerprinting?
Restrictive enzymes, when mixed with DNA, cut molecules at different lengths based on their genetic code. For example, one specific enzyme will cut the DNA when the code "GAATTC" is read. Since everyone's DNA is different, the lengths of these cut sections will differ as well.
3. What is the function of the agarose gel electrophoresis step?Agarose gel electrophoresis acts as a "molecular strainer", sorting the longer strands of DNA from the shorter strands by the use of positive and negative charges. The shorter strands of DNA will move through the gel much more quickly than the longer strands.
4. Why is a nylon membrane used to blot the DNA?
The nylon membrane is much easier to handle and work with than the agarose gel, and makes viewing the DNA more manageable.
5. What does a dark spot on the X-ray film indicate?
The dark spots on the film represent where the probes sat, attached to the DNA. Together, the spots form the DNA fingerprint.
For the second part of this activity, we are going to use this source. We are going to analyze the case of Ronald Cotton's wrongful conviction, as well as the case of O.J. Simpson.
6. What evidence was initially used to convict Cotton?
Originally, an eyewitness account was used to convict Cotton. When the victim had to identify her attacker, he was not in the line up of suspects, so she selected the person who bared the closest resemblance, which was Ronald Cotton.
7. What did the DNA evidence show?
By using DNA evidence, it became clear that Cotton was innocent, as well as the fact that often times, witnesses are unreliable. This has led to prevention of wrongfully convicting the innocent in the present.
8. How could DNA fingerprinting be used to prevent a false conviction if a case like this was being tried today?
DNA fingerprinting eliminates the chances of convicting the wrong person by ensuring correct identification. It ties a specific person to the scene of a crime without a doubt.
9. What percentage of convicts are unjustly convicted of sexual assault cases, according to Neufeld and Scheck?
According to Peter Neufeld and Barry Scheck, approximately 25% of convicts are unjustly convicted of sexual assault.
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?
Both Neufeld and Scheck believed that O.J Simpson's case showed potential for DNA evidence in forensic cases, however, when the technology is mishandled, it is not useful in the case. When presenting DNA evidence, there can be no room for error.
Overall, DNA evidence has proven very useful in multiple cases, both cold and current. It is amazing to see how science can be applied in different fields, as well as how far technology has advanced.
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