Your body is made up of ~ 60 trillion cells. These cells are little factories that perform the work your body requires such as storing energy, making hormones, making enzymes to help digest your food, and more.DNA (a.k.a. deoxyribonucleic acid) is the recipe for how to make an organism and the instructions for each cell to know what to do. So you have tiny recipe cards in most of the cells of your body that give the exact formula for how to make one of you! DNA can also be used as an identifier as no two individuals have the same DNA makeup - well, that is, unless you are identical twins!
In every living thing (plant or animal) are these recipes or sets of instructions made up of shorter
segments called genes. The genes provide the instructions on what is the plant or animal, what it looks like, how it behaves, how it is to survive, and how it will interact with its surrounding environment.
The genes are strung together in long stands of DNA and these strands are called chromosomes. Most living organisms inherited a copy of DNA from each parent - one from dad and one from mom. These strands come together and 'fight it out' as to which genes will win and guide your looks, functions and behaviors! Therefore, most organisms have pairs of chromosomes in most of their cells with reproductive cells and red blood cells being the exceptions). In humans, we have 23 pairs of chromosomes and a lowly fruit fly has only 4 pairs! Poor fruit fly!
What if mom gave you the gene for brown eyes and dad gave you the gene for green eyes? Well,
these different versions of genes are called alleles. You have a pair of alleles for each trait and one of them will typically 'win the fight' and be expressed in the organism. Brown eyes is the dominant allele that always wins the fight! The green eyed allele is recessive and if there is a dominant allele present, the green eyes won't be expressed - they are 'silenced!' They're still there in the DNA code but nobody will ever know...that is, until you have a green eyed child! (This is a simplified example - eye color is governed by more than one gene.)
Just like an alphabet makes up sentences, each gene is made up of combinations of four different
types of chemicals called nucleotides. Just like words, it is the combinations of the nucleotide bases that determine everything about a living organism!
The four nucleotides are called:
- cytosine (C)
- guanine (G)
- thymine (T)
Let's see an example:
The gene for brown eyes might have this nucleotide sequence.
The gene for blue eyes might have this nucleotide sequence.
Notice how the nucleotide sequences below are very similar. The only difference being the last three bases. Both of these codes are giving information on how to make the eye but the last three tell what color to make the iris of the eye. Now this was only an example - if you were really looking at the DNA sequence for eye color, it would be several thousand nitrogenous bases long!)
APPLYING YOUR DNA KNOWLEDGE TO THE CRIME SCENE...
- DNA is found in nearly every cell of the body. Hair follicles, skin, saliva (saliva picks up dead cells from the mouth and glands), and blood (the white blood cells) are common sources for evidence at the crime scene. A single hair follicle, a licked stamp or a single drop of blood is all you need to perform an analysis and catch your criminal!
- Once you find DNA evidence at the crime scene, great care needs to be taken to keep it from degrading! DNA samples need to be placed in adequately dried or frozen containers until the analysis can be performed.
- The information in the non-coded region of DNA: the total amount of DNA in a cell is called the genome. Only about 5% of this contains vital instructions on how to make and run the factory of 'you.' The other 95% is like 'junk mail.' But is it really junk in a criminal investigator's eyes? NOPE! There are variable regions (polymorphisms) that vary in length as well as base sequence. We use these variations to make a DNA fingerprint.
- Polymorphisms is a fancy word indeed! Alec Jeffreys, in 1985, discovered that there are segments in a DNA molecule that are unique to each person . If you analyze these segments, you can distinguish between one person and another. We call this 'DNA Fingerprinting' or 'DNA Typing' and this is what is used to make a match between a suspect and a crime scene.
- Variable Number Tandem Repeats (VNTRs): the same base sequence that repeats throughout a specific region in a strand is called a VNTR. These can be hundreds of base pairs long and repeat a variable number of times.
- Short Tandem Repeats (STRs): Shorter than VNTRs, STRs repeat as well but are only 3 to 7 base pairs in length. STRs repeat over segments of DNA that are as long as 350 or more bases.
LET'S PREPARE A SAMPLE OF DNA
- Extract the DNA from the sample: this is using chemical agents to separate the DNA (without harming or altering it) from the sample.
- Cutting or Amplifying the DNA: you want to determine the VNTR or STR sequences in any given locus (segment) of the DNA strand. Several methods are available but the most common is 'restriction fragment length polymorphism' or RFLP) which is using enzymes to chop it up into specific fragments and then PCR (polymerase chain reaction) might be necessary which is simply amplifying a small sample when there is not enough.
- Now you have fragments, you need to separate these fragments by separating them in a viscous gel with an electrical current passed through and the fragments will separate based upon their charge (DNA is negatively charged) and their size. The larger fragments will be slower to move through the gel and will separate from the quicker moving short fragments!)
- Now you've got separated fragments, you'll need to transfer them to a nylon membrane. This is called a Southern Blot - named for the researcher who discovered it - not because it was only done in the South! So you'll put a nylon membrane on top of the gel and kind of like soaking up liquid with a sponge - the bands of DNA will transfer onto the nylon membrane.
- Allright, you've got the DNA fragments, separated, and stuck on a membrane. Now what? You want to look at them and take a picture! But first, you have to tag them with something you can look at! You can view the bands of DNA by tagging them with radioisotopes (radioactive chemicals) that attach to the fragments.
- Now, look at your tagged fragments! Using an autoradiograph, or autorad, you can view and make a picture of these awesome DNA bands and compare to a known sample of known weight as well as your unknown sample from the crime scene!
DNA video simple science
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Gel Electrophoresis and Forensic Science: Biotechnology Science Fair Project
http://www.sciencebuddies.org/science-fair-projects/project_ideas/BioChem_p028.shtml In this Biotechnology Project Idea, the Science Buddies Summer Science Fellows demonstrate how to construct your own gel electrophoresis chamber, the technology behind DNA analysis, and use it to compare molecules in different colors of food coloring dye. You can see the full science experimental procedure for this science fair project idea—and do it yourself!—in 'Forensic Science: Building Your Own Tool for Identifying DNA' project idea at Science Buddies. This includes details on construction, variables, and data collection as well as guidelines on developing the experiment into a full science fair project. Science Buddies also hosts a library of over 1000 other free science fair project ideas. Project Category: Biotechnology
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How do we tell people apart by using their DNA? From murder investigations to paternity testing, DNA fingerprinting is an essential tool in the modern world. But how is it carried out? Find out in the latest Naked Science Scrapbook!More videos and podcasts from http://www.thenakedscientists.com
Paul Andersen describes the process of DNA fingerprinting and DNA profiling. He explains how variability in STRs can be used to identify individuals. He explains the importance of DNA fingerprinting in forensics and paternity cases. Intro Music Atribution Title: I4dsong_loop_main.wav Artist: CosmicD Link to sound: http://www.freesound.org/people/CosmicD/sounds/72556/ Creative Commons Atribution License
History Channel on the Early Implementation of DNA in Forensic Science.mp4
History Channel on the Early Implementation of DNA in Forensic Science. From its beginnings to CODIS. The Timothy Spencer Case, DNA Data Banks, Paul B. Ferrara, Innocence Project, and Early Backlogs, ect.
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DNA evidence is the strongest and most reliable identification evidence that exists in crime investigation. Dr. Jobin discusses how the technology has advanced, how much DNA is needed for a positive identification, and whether or not DNA evidence can be used for cold cases. For more videos like this visit www.booked.tv
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DNA Forensics from Life Technologies -- Because It Matters
To learn more, visit http://www.lifetechnologies.com/hid In forensic DNA labs around the world, the stakes are higher than ever. That's why Life Technologies remains focused on providing the most reliable and efficient solutions for human identification, backed by the most extensive global network of training and support. Because when people are counting on you, you need a partner you can count on.
The PCR Song
"Scientists for Better PCR" a Bio-Rad Music Video for the all new 1000-Series Thermal Cyclers Click below for more information: http://bio-rad.cnpg.com/lsca/videos/ScientistsForBetterPCR/