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DNA Facts

DNA Facts. Watson & Crick 1953 Contains all Genetic info ½ from each parent ¾ like siblings Double helix Unique????? In all cells with nuclei Made of nucleotides with nitrogen bases ATCG 98.5% is Junk… non-coding DNA, that’s what makes you unique Also found in mitochondria…from mom.

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DNA Facts

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  1. DNA Facts • Watson & Crick 1953 • Contains all Genetic info • ½ from each parent • ¾ like siblings • Double helix • Unique????? • In all cells with nuclei • Made of nucleotides with nitrogen bases ATCG • 98.5% is Junk… non-coding DNA, that’s what makes you unique • Also found in mitochondria…from mom

  2. Sources of DNA • Blood • Saliva • Semen • Vaginal fluid • Skin cells • Hair with follicle

  3. Obtaining DNA from a suspect • A warrant is needed • Garbage can be used……. • Tissue, coffee cup, straw • Certain convicted felons in NYS must submit DNA sample • Since January 1, 1996, the law in New York State has required offenders convicted of certain felonies to submit biological samples (formerly blood and more recently buccal samples swabbed from the inside of the cheek) for DNA profiling through laboratory analysis. • The resulting records of offender DNA profiles are organized into a centralized index within the State DNA Data Bank—a part of CODIS, the national Combined DNA Index System developed by the FBI.

  4. CODIS… • Combined DNA INDEX System • DNA database funded by the United StatesFederal Bureau of Investigation (FBI). • It is a computer system that stores DNA profiles created by federal, state, and local crime laboratories in the United States, with the ability to search the database to assist in the identification of suspects in crimes. • Congress formally authorized the FBI to operate CODIS and set national standards for forensic DNA testing. Although the Act was passed in 1994, CODIS did not become fully operational until 1998.

  5. Creating a DNA Profile • Extraction • Use of Restriction Enzymes • Amplification • Electrophoresis

  6. Extraction • DNA is extracted from the cells • Strong detergents are used to remove the DNA from the membranes that hold it.

  7. You can do DNA extraction at home… • All the materials and equipments to carry out the experiment are items commonly found in the household. • Pour 3/8 cup of water into a cup. • Add 1/4 teaspoon of salt and clear liquid soap into the cup, and stir for the salt to dissolve. The soap causes the cell walls to break up, freeing the DNA inside. The salt is for keeping the DNA molecules together. • Place the organic materials into the sandwich bag or blender and mash or crush until completely pulverized. This is to break the cells apart. • Add 2 teaspoons of the soap-salt solution to the bag. Mix gently by compressing or rocking the bag for at least 1 minute. • Pour the mixture through coffee filter into a clear jar. Let it drain into the jar for 10 minutes.

  8. DNA extraction at home • Meanwhile, pour 1/4 coup of rubbing alcohol into another clear jar and put the jar in the freezer or a bowl of ice. The alcohol helps strip the water molecules from the outside of the DNA molecules, causing the molecule to collapse on itself and separate from the proteins in the solution. • After 10 minutes have elapsed, pour the strained liquid into the alcohol. Let the jar sit still for at least 5 minutes. The final product contains a layer of proteins and a cloudy layer of DNA clumped together. The naked eyes cannot resolve the individual macromolecules within.

  9. Use of Restriction Enzymes • Used to cut the DNA into shorter fragments • The enzymes cut the DNA at a specific sequence of bases (recognition site) • These fragments are called VNTRs (variable number tandem repeats) and STRs (short tandem repeats)

  10. Use of Restriction Enzymes

  11. VNTRs • short sequences of DNA that contain 9-80 bases with a repeated sequence • ex. CATACAGAC CATACAGAC CATACAGAC • In one person it might repeat 3x in another 7x

  12. STRs • More useful in DNA analysis • Shorter than VNTRs • 2-5 bases repeated • Ex. GATA GATA GATA GATA GATA • More accurately used, easier to separate • Degraded DNA can also be analyzed

  13. Amplification • PCR (polymerase chain reaction) used to amplify the amount or DNA Generates multiple identical copies of small amounts of DNA • Billions of copies of the DNA sample can be made in a few hours • Invented in 1993 by Dr. Gary Mullis • Used in Jurassic Park

  14. PCR

  15. Electrophoresis • Separates the DNA fragments by size and polarity in an electric field • The DNA moves through the field by size, smaller fragments move more quickly through the gel • The fragments form band with the shortest fragments closest to the (+) end

  16. Gel Electrophoresis Apparatus

  17. Electrophoresis

  18. The RESULTS……..

  19. Uses of a DNA profile • Match Crime scene DNA to suspect’s DNA • Eliminate suspects • Paternity/maternity tests • ID family members • ID human remains • Free those falsely accused

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