DNA Fingerprinting

DNA Fingerprinting

DNA Fingerprinting…What is it? A DNA fingerprint is a picture of what your DNA looks like. Your fingerprint looks different than anyone else’s. (Unless you’re an identical twin.) Before we learn about fingerprinting, let’s review DNA…..

DNA is The MOLECULE Of HEREDITY

What is DNA? • Genetic Material that determines an Organism’s Traits. • Controls traits by producing PROTEINS. • Within the structure of DNA is the complete information for making all the proteins for an organism. Deoxyribonucleic Acid

DNA is made of repeating units called NUCLEOTIDES! A ring with one or more atoms of nitrogen The sugar is called Deoxyribose Sugar

The Structure Of One Nucleotide. Phosphate Sugar Nitrogen Base

The Nucleotides join together to form a long chain. P S N.B. P S N.B. P S N.B. P S N.B.

Pictures of DNA P P S S NB NB P P S S NB NB P P S S NB NB P P S S NB NB P Photo From: http://www.ch.cam.ac.uk/SGTL/Structures/nucleic/n2.html P

Purines Adenine Guanine Pyramidines Thymine Cytosine DNA has 4 possible Nitrogen Bases

Base Pairs.A’s & T’s C’s & G’s • This picture shows how the nitrogen bases bond. • When they bond they are calledComplementary Base Pairs

Here is One Half of a DNA strand.Complete this strand by drawing the complementarybase pairs & the rest of the nucleotides. P P S S A T P P S S C G P P S S G C P P S S T A P P S S C G P P

DNA the Tattle-Tale Although the structure of DNA is the same throughout all species of plants, animals, and microorganisms, each individual organism looks different. This is due to the order of the base pairs (A,T,C,G). Not only does this order make you a human rather than a dog or a daffodil, it also makes you unique. The order of your DNA is different from everyone else, but every cell in your body has that same order. So, your hair, blood, skin and all of the other cells in your body are exactly the same – but different from everyone else. This comes in very handy when police are investigating a crime. If a person left a strand of hair, a drop of blood, or any other cells at a crime scene, the police will know that person was there.

But, How does it Work? Two randomly chosen people from anywhere on Earth are expected be 99.9% genetically identical. So how can one person's DNA be unique enough to identify him or her as the perpetrator of a particular crime? The answer, it turns out, is volume: the human genome is composed of three billion base pairs! Even at 99.9% similarity, any two people will still differ at about three million base pairs. In fact, no two people on Earth have exactly the same genetic sequence, except identical twins.

Two different DNA tests exist.Both are very accurate, but use different methods. 1. RFLP Restriction Fragment Length Polymorphism 2. PCR Polymerase Chain Reaction After the DNA test is completed, a second test is required called the Southern Blot

RFLP – Restriction Fragment Length Polymorphism • more accurate than PCR • requires a large sample of fresh DNA • takes longer than PCR • when a match is found, there is no question as to whether the suspect was at the scene Back to DNA tests

PCR – Polymerase Chain Reaction • not as accurate, takes less time, less costly • requires only a small sample • that sample is amplified using polymerases to force the small amounts of DNA to copy themselves many times • can be performed on older samples • PCR only analyzes a specific gene, which is analyzed to find matches • If no match is found, the donor was not at the scenes, however a match doesn't prove conclusively the person was there - many people may have the same match Back to DNA tests

Steps to Southern Blotting • Isolation of DNA • Cutting Sizing, and Sorting • Transfer of DNA to Nylon 4-5. Probing 6. DNA Fingerprint

Step 1: Isolation of DNA DNA must be recovered from the cells or tissues of the body. Tissue like blood, hair, or skin can be used. Only a small amount of tissue is needed. For example, the amount of DNA found in one drop of blood or in one hair root is enough. Back to Blot Steps

Step 2: Cutting, Sizing, and Sorting Special restriction enzymesare used to cut the DNA at specific places. The DNA pieces are sorted according to sizeby a technique called electrophoresis. The DNA pieces are passed through a gelmade from seaweed agarose (a jelly-like product made from seaweed). This technique is like screening sand through progressively finer mesh screens to determine particle sizes. Back to Blot Steps Photo From: http://www.biologycorner.com/bio4/notes/DNA_fingerprint.php

Step 3: Transfer of DNA to Nylon The DNA pieces are transferred to a nylon sheet by placing the sheet on the gel and soaking them overnight. Gel with DNA pieces from PCR or RFLP Nylon Sheet “blotting up” the pieces Back to Blot Steps Photo From: http://www.bio.miami.edu/dana/250/25005_8.html

Steps 4-5: Probing Adding radioactive or colored probesto the nylon sheet produces a pattern called the DNA fingerprint. Each probe typically sticks in only one or two specific places on the nylon sheet. Colored Probes Bind to Certain Sequences in the DNA Pieces and Stains Them X-Ray film is put over the Nylon Sheet so we can View the Results Back to Blot Steps

Step 6: DNA Fingerprint The final DNA fingerprint is built by using several probes (5-10 or more) simultaneously. It resembles the bar codes used by grocery store scanners. Photo from: http://www.nottingham.ac.uk/biology/contact/academics/dyer?N=D Photo From: http://fig.cox.miami.edu/~cmallery/150/gene/mol_gen.htm Back to Blot Steps

Police use the fingerprints to compare a suspect’s DNA to the DNA found at a crime scene.

Who Done It? Use these DNA fingerprints to determine which suspect committed the crime. Photos From: http://www.biologycorner.com/bio4/notes/DNA_fingerprint.php

References • http://www.biologycorner.com/bio4/notes/DNA_fingerprint.php • http://www.scq.ubc.ca/a-brief-tour-of-dna-fngerprinting/ • http://evolution.berkeley.edu/evolibrary/news/060301_crime

DNA Fingerprinting