Forensic Science 2

The DNA Molecule  DNA is what makes genes  DNA stands for deoxyribonucleic acid  It is a molecule that makes up genes and determines the traits of all living things  All living things contain DNA in their cells  The structure is similar to that of a ladder Ladder Upright Ladder Rung

The DNA Molecule  Six features of the DNA model Two main sides (similar to the ladder) Sides are made of alternating sugar and acid molecules Parts connect the sides together (similar to the rungs of a ladder) called nitrogen bases There are 4 types of nitrogen bases: adenine (A), cytosine (C), thymine (T), guanine (G) The four bases join together in certain ways The “ladder” is twisted in a spiral called a double helix

The DNA Molecule  Nitrogen bases: Adenine always pairs with thymine Guanine always pairs with cytosine They fit together similar to that of a puzzle  All your DNA comes together to form chromosomes  Remember: chromosomes are found in the nucleus of cells and your body is made entirely of cells

Hoe DNA Works  DNA is a code for life  So, the code determines if the organism is a plant or animal, is tall or short, have dark or light hair and every other unique thing we see in life  Example: GAGTGAGGCTTC CTCACTCCGAAG This is a code

How DNA Works  The code is read similar to how you read a sentence  The code starts on the right and continues reading until a stop code is reached  For example: you read and understand each word and when you reach a period (.) you know the sentence is complete.  The code gives the cell information it needs to function

Making Proteins  Remember: your cells have ribosomes, which make proteins & ribosomes are located in the cytoplasm (not the nucleus where the DNA is found)  DNA codes for the proteins that the ribosomes make  There has to be a messenger to relay information from the DNA (in the nucleus) to the ribosomes (in the cytoplasm)

Making Proteins  The messenger is called ribonucleic acid or RNA  Types of RNA Messenger RNA (mRNA) Transfer RNA (tRNA)  The DNA copies it’s information onto the mRNA and the mRNA travels out of the nucleus into the cytoplasm where the ribosome is and give the information to the tRNA

How DNA Copies Itself to RNA  Think about the ladder model of DNA again  The ladder breaks apart into 2 sides  A strand of RNA attaches itself to the DNA and makes a copy of the code – the only difference is RNA does not have the nitrogen base thymine (T), but has uracil (U) which pairs with adenine (A)  Example: AACGTTT DNA UUGCAAA RNA

How DNA Copies Itself to RNA  The copied mRNA detaches from the DNA  The DNA closes back up  The mRNA moves out of the nucleus into the cytoplasm  The mRNA attaches to the ribosome and gives the information tRNA to make the proteins

History of DNA Investigation  Was introduced in the mid-1980s  Revolutionized forensic science and the ability of law enforcement to match perpetrators with crime scenes  Known as 'DNA fingerprinting' or DNA typing (profiling)

History of DNA Investigation  Discovered by an English geneticist named Alec Jeffreys  Found that certain regions of DNA contained DNA sequences that were repeated over and over again  He also discovered that the number of repeated sections present in a sample could differ from individual to individual

History of DNA Investigation  The past 15 years have seen tremendous growth in the use of DNA evidence in crime scene investigations as well as paternity testing  Today over 150 public forensic laboratories and several dozen private paternity testing laboratories conduct hundreds of thousands of DNA test annually in the United States

Gathering DNA Evidence  All biological evidence found at crime scenes can be subjected to DNA testing  For example, hair, skin, some bodily fluids, blood, etc  Samples such as feces and vomit can be tested, but may not be routinely accepted by laboratories for testing  Only a few cells can be sufficient to obtain useful DNA information

Gathering DNA Evidence EvidencePossible Location of DNA on the Evidence Source of DNA baseball bat or similar weapon handle, endsweat, skin, blood, tissue hat, bandanna, or mask insidesweat, hair, dandruff eyeglassesnose or ear pieces, lens sweat, skin facial tissue, cotton swab surface areamucus, blood, sweat, semen, ear wax EvidencePossible Location of DNA on the Evidence Source of DNA fingernail, partial fingernail scrapingsBlood, sweat, tissue tape or ligature inside/outsid e surface skin, sweat bottle, can, or glass sides, mouthpiece saliva, sweat

Gathering DNA Evidence EvidencePossible Location of DNA on the Evidence Source of DNA dirty laundrysurface areablood, sweat, semen toothpicktipssaliva used cigarette cigarette buttSaliva stamp or envelope licked areaSaliva EvidencePossible Location of DNA on the Evidence Source of DNA used condom inside/outsid e surface semen, vaginal or rectal cells blanket, pillow, sheet surface areasweat, hair, semen, urine, saliva "through and through" bullet outside surface blood, tissue bite markperson's skin or clothing saliva

Gathering DNA Evidence  Contamination - Because extremely small samples of DNA can be used as evidence, greater attention to contamination issues is necessary when identifying, collecting, and preserving DNA evidence.  DNA evidence can be contaminated when DNA from another source gets mixed with DNA relevant to the case.

Storing DNA Evidence  Direct sunlight and warmer conditions may degrade DNA  Avoid storing evidence in places that may get hot, such as the trunk of the police car  To best preserve DNA evidence, store in a cold environment

Analyzing DNA Evidence  The general procedure includes: 1) isolating DNA from evidence sample containing DNA of unknown origin (at a later time, the isolation of DNA from a sample (e.g., blood) from a known individual or suspect) 2) processing DNA so that test results may be obtained

Analyzing DNA Evidence  The general procedure includes: 3) determination of the DNA test results (or types), from specific regions of the DNA 4) comparison and interpretation of the test results from the unknown and known samples to determine whether the known individual is not the source of the DNA or is included as a possible source of the DNA.