To start the process police collect traces of body

Info icon This preview shows pages 2–3. Sign up to view the full content.

To start the process, police collect traces of body cells from a crime scene. They also select cells from suspects, often through the drawing of blood. DNA is then extracted from each cell sample and replicated through a polymerase chain reaction (PCR). After scientists make numerous copies of the DNA, they test it with restriction enzymes, which cut it at specific sequences called restriction sites. They are left with different-sized pieces called restriction fragment length polymorphisms, or RFLPs. RFLPs are studied by gel electrophoresis. This is accomplished by applying an electric current to a gel containing the DNA, which causes the fragments to separate by size. Scientists then apply a weak acid to a gel that allows the fragments to be blotted onto a paper. Lastly, the DNA is developed into an image by exposing the paper to X-rays. Once the image is developed, sequences are compared to find if the DNA of any suspect matches that found at the crime scene. In 1987, Dr. Alec J. Jeffreys was tasked with performing the first fingerprint analysis accepted in a criminal case. He helped convince the court that British Robert Melias was guilty of rape against a disabled woman. Evidence was gathered by a semen stain on her clothes, which
Image of page 2

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern