40. DNA fingerprinting is used in many situations to help identify individuals. Analyze the situation below before answering the questions that follow.
A man was attacked and robbed, but remembers nothing of the incident because he fell and hit his head. He has numerous cuts and abrasions from the event, and blood was found under his fingernails. A piece of torn clothing with a bloodstain on it was also found at the scene.
Two people were seen near the crime scene. Both males, they say they don't know each other and just happened to be near the scene at the time of the attack. One of the males has a fresh scratch across his face, while the other male has a scratch on his right arm.
It's not clear from observations of the crime scene how many individuals were involved in the crime. Two males have reportedly been robbing individuals in the vicinity. There's a rumor that the two are brothers.
a. Explain two DISTINCT uses that DNA fingerprinting could be used for in this situation. In particular, what are two important issues that should be resolved to help clarify the identity of the individuals of the body fluids found at the scene?
b. How could you test one of these issues using DNA fingerprinting without using blood samples from the scene of the crime?
a. Two distinct uses of DNA fingerprinting in this situation could be:
1. Identifying the perpetrator(s): DNA fingerprinting can be used to compare the DNA profile obtained from the blood found under the victim's fingernails and the bloodstain on the torn clothing with the DNA profiles of the two suspects. If the DNA profiles from the crime scene match the DNA profile of one of the suspects, it could indicate that person's involvement in the crime.
Important issues to be resolved include:
- Ensuring the integrity of the DNA samples: The samples collected from the crime scene should be properly handled and preserved to prevent contamination or degradation, which could potentially affect the accuracy of the DNA analysis.
- Establishing the allelic frequencies: It is crucial to determine the likelihood of finding a particular DNA profile in a given population. By comparing the DNA profiles of the suspects with the general population database, the rarity or commonness of the DNA profile can be assessed, providing a stronger indication of their involvement.
2. Determining the relationship between the suspects: Since there is a rumor that the two suspects may be brothers, DNA fingerprinting can be used to establish their biological relationship. By comparing their DNA profiles, particularly by analyzing specific DNA markers that are commonly used for kinship testing, it can be determined if they share a high degree of genetic similarity, indicating a potential sibling relationship.
Important issues to be resolved include:
- Collecting reference samples: DNA samples need to be obtained from both suspects to create their respective DNA profiles. This requires the cooperation and consent of the individuals involved, as well as ensuring the proper chain of custody and sample collection procedures to maintain the integrity of the samples.
- Appropriate statistical analysis: The DNA testing results should be subjected to appropriate statistical analysis to determine the probability of the two individuals being full siblings or related in some other manner. This helps in establishing the strength of the genetic evidence.
b. To test the issue of determining the relationship between the suspects without using blood samples from the scene of the crime, alternative DNA sources can be used. For example, DNA samples can be obtained from the suspects' saliva through saliva swabs or from discarded items like cigarette butts, drinking cups, or chewing gum. These samples can provide sufficient DNA material for DNA fingerprinting analysis, allowing for the comparison of their genetic profiles and determining the likelihood of a familial relationship.
a. DNA fingerprinting can be used in this situation for two distinct purposes:
1) Identification of individuals: DNA fingerprinting can help identify the individuals involved in the crime by comparing the DNA profiles obtained from the body fluids found at the crime scene with the DNA samples collected from potential suspects. This can help determine if any of the individuals present at the scene match the DNA profiles recovered from the evidence.
Two important issues that should be resolved to help clarify the identity of the individuals from the body fluids found at the scene are:
- Matching the DNA profiles: The DNA profiles obtained from the body fluids should be compared with the DNA samples of the two males seen near the crime scene. If any of the DNA profiles match, it would provide strong evidence linking that individual to the crime.
- Determining the number of individuals involved: It is not clear from the crime scene observations how many individuals were involved in the crime. DNA fingerprinting can help in determining if there are DNA profiles from more than two individuals in the body fluids, which would suggest the involvement of additional perpetrators.
2) Establishing a familial relationship: There is a rumor that the two males seen near the crime scene are brothers. DNA fingerprinting can be used to determine if there is a genetic relationship between the individuals. By comparing their DNA profiles using specific markers known as genetic markers, it can be determined if they share a common biological parent or if they are unrelated.
b. To test the issue of establishing a familial relationship using DNA fingerprinting without using blood samples from the scene of the crime, alternative sources of DNA can be collected from the individuals involved.
One such source could be the collection of buccal swabs. Buccal swabs are non-invasive and can be easily obtained by swabbing the inside of the cheek with a sterile cotton swab. By obtaining buccal swabs from the two males, their DNA profiles can be generated and compared using genetic markers to determine if there is a genetic relationship between them, supporting or refuting the rumor that they are brothers.