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    DNA Profiling Technology

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    A man and his wife were on vacation in Paris. On the way back to the hotel, they were approached by two men with weapons who demanded their jewelry. A physical interaction occurred in which the robbers violently wrestled the man to the ground and removed his watch and rings while his wife tried to run away. The man and his wife were shot and killed. The bodies of the two victims were pulled into an alley. Multiple scratches were on the body of the male victim, and blood was also found on the female victim because the robbers tore the necklace, rings, and earrings off that she was wearing. The two men committing the crime both had previous records for assault and robbery. How were the men convicted of the crime?
    Address the following
    What exactly is DNA profiling? Explain in detail.
    How it is used to solve crimes? Explain in detail.
    Regarding the case above:
    What physical evidence would be retrieved from the crime scene?
    Identify each item of physical evidence, and fully justify your decision to collect it as evidence.
    What type(s) of DNA tests are required to investigate the crime you have chosen? Explain in detail, and fully support your argument.
    What is the testing process for the technique(s) used to test each piece of evidence? Be specific, and explain in detail.
    After analyzing the evidence, explain how the evidence convicted the suspects.
    Be sure to reference all sources using APA style.

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    Solution Preview

    Below I have explained in details DNA profiling and how evidences are collected, different tests runs and how all those are used to tie suspects to a crime scene. You can take out what's relevant to answer your questions.

    DNA profiling relates to the procedure where a small set of DNA variations that are very likely to be different in all unrelated individuals are exploited by forensic investigators to discriminate one individual from another. This technique was originally developed by Alec Jeffreys from the Leicester University in the year 1985. Short Tandem Repeat sequences (STR) are used these days to profile a person's DNA. STR analysis has made this technique extremely sensitive and even trace amount of skin cells, hair or a tiny drop of blood (even dried blood) is required to run the test and get confirming results. The applications of this method are plenty, following are some of the areas this technique is employed:
    • In forensic and criminal investigation DNA is used to link a person to the crime scene from samples like blood, hair left by the criminal. DNA profiles of repeat offenders are kept by the police to link them to any crime scene.
    • DNA is also used in matching the DNA of parents to their child. A paternity test is the most definitive way of confirming a child's paternity.
    •DNA testing can be used to search ancestors. People can track their long lost relatives via DNA testing.

    DNA Profiling process:

    99.9% of the human DNA sequences are same in every person but there is also a considerable amount of DNA (the remaining 0.1 percent of the genome—3 million nucleotide bases—for telltale variations) that is different between people. DNA profiling technique exploits this variance to discriminate between different individuals.
    In order to link a criminal to a crime scene, a single droplet of blood or stray eyelash collected at a crime scene is all that is required by investigators since it carries all the genetic information of an individual. Once the evidence is taken back to the lab the following steps are undertaken:

    1. DNA extraction: DNA is first extracted from the sample (blood, hair or semen). As little as 100μg (microgram) of DNA is required by forensic experts to construct a DNA profile from the samples retrieved at the crime scene. Just to give an idea how little 100μg of DNA is, imagine a few cells of saliva left on a straw while drinking a soda or a tiny blood smear left in the crime scene which belongs to the murderer or skin cells collected inside the nails of the victim during struggling or one strand of hair found inside the hand of the victim belonging to the suspect, should be sufficient to extract that amount of DNA to profile the criminal.
    2. DNA Amplification by Polymerase Chain Reaction (PCR): Once the DNA is extracted from the sample, this DNA needs to be amplified. DNA has coding sequences and non-coding sequences. Coding sequences code for functional proteins whereas non-coding sequences have no role in protein expression. Short Tandem Repeat (STR) sequences are 4-10 nucleotide sequences that are present in these non-coding region of a person's DNA. Each and every individual have unique STR sequences, which means the nucleotide numbers vary from one individual to another. More genetically close two individuals are the similar the STR sequences become but non-related individuals have very different STR sequences. For DNA profiling investigators use ~13 different types of STR sequences. Using DNA primers, each of these STR sequences are amplified. During PCR, fluorescent dyes are attached to all the STR copies that get made—one type of dye ...

    Solution Summary

    The solution explains DNA profiling technology and how it is used by forensic experts to connect previous offenders whose DNA profile is stored with the police to connect them to a crime scene. It also explains Short Tandem Repeat technique and how to collect different evidences left by criminals at the crime scene.