We did our first labs for our CSI class. This class will need a little prior preparation, but it was well worth it because the kids were very interested and kept to task the entire period.
Preparing for Class:
|The chromotography demonstration set-up.|
- Prepare chromotography strips for the class. Take the pen you used for the note and another pen and make chromotography strips for them. Instead of a second pen, to make sure the strips are dissimilar, you can use ink from a jar of ink used in pen and ink projects or you can make your own ink by mix together 1/2 tea. red food color and 1/4 tea. green food color.
|from Mystery Science; Part III: Ink Chromotography (If you want to do the experiment yourself)|
Make a dot of the ink from the ink used to write the note on one 1-inch x 3 inch rectangle of paper towel. Make a similar dot of the second ink on an identical 1-inch x 3 inch rectangle of paper towel. Label each strip with a pencil. Tape the strips each to a pencil or craft stick. Set these sticks over the rims of two glasses of water so that the water touches the strips and climbs up the strips. When the water moves through the dots, the ink should separate. They should separate in a different manner. If they don't, then choose another type of ink for your second sample. You want them to look noticeably different.
- Prepare the DNA fingerprints. To prepare someone's DNA fingerprint, cells are removed from that individual and the DNA is extracted from those cells, then cut into small pieces with restriction enzymes. Because everyone's DNA is different, restriction enzymes cut everyone's DNA into different sizes and numbers of pieces. By analyzing the DNA pieces, an investigator can distinguish one individual from another. To look at these pieces, the DNA fragments are loaded onto a gel and then are exposed to an electrical field that causes the fragment to travel through the gel. The rate and distance at which fragments can travel through the gel depends on their size. Eventually the fragments form invisible bands throughout the gel. These DNA bands are then transferred to a nylon membrane. Radioactive DNA probes are added to the membrane, then x-ray film is placed over the radioactive probes on the membranes. When the x-ray film is developed, the radioactive probes have exposed it in places where there is DNA. This film makes a DNA print. As you can see, completing this process in a class lab would be difficult (although not impossible -see below) and so you will need to draw some fictitious DNA fingerprints. On a thin strip of white paper, draw a series of thick, medium and thin lines with gaps of various widths between them. Make two copies of one (one for the perpetrator and one that the lab will give to your CSIs) and different ones for the other suspects.
- Prepare handwriting samples. Have four people, including the person who wrote the note, give a handwriting sample, even if it is just a signature on the statements (see below.)
- Read and analyze the suspect's statements. I wrote out statements of each of the suspects. They were a little lengthy to put in this post, but if you are interested in doing this scenario, I can send them to you. (NOTE: I HAVE SINCE LOST THESE DURING S HIME RENOVATION PROJECT AND CANNOT SEND TO ANYONE. I AM SURE YOU CAN MAKE UP STATEMENTS THAT WILL FIT. JUST THROW IN A COUOLE OF RED HERRINGS!) The pertinent facts were that a brown pen was found in the kitchen and another in Professor Plum's front pocket. Each of the statements were signed. Analyzing the statements for clues may take a bit of time, so work through it slowly.
- Perform chromotography lab on the ink from the brown pens. Your students will now perform the same lab as you did with the two inks, with the ink from the mysterious note. Which ink is it more like once it begins to divide? Can you identify which pen the ink came from. Who does this implicate?
- Identify the DNA fingerprint from the hair in the comb. Explain the process of DNA fingerprinting and then show your students the DNA fingerprint you made that the lab will give to your students. Show them the DNA fingerprints from all the suspects. Have them compare them and match the DNA fingerprint from the lab to the matching one among the suspects. What does this clue tell us?
- Analyze handwriting samples. Have your students compare the handwriting samples to that of the mysterious note. There are twelve basic characteristics your students can look for when comparing handwriting. They can circle where they see similarities in the samples. Which one has the most comparisons to the note? What does this tell us?
- Line quality: Do the letters flow or are they written with very intent strokes?
- Spacing of words and letters: What is the average space between words and letters.
- Ratio of height width and size of letters: Are the letters consistent in height, width and size?
- Lifting pen: Does the author lift his pen to stop writing a word and start a new word?
- Connecting strokes: How are capital letters connected to the lower case letters?
- Strokes to begin and end: Where does the letter begin and end on a page?
- Unusual letter formation: Are any letter written with unusual slants or angles? Are some letter printed rather than written in cursive?
- Pen pressure: How much pen pressure is applied on upward and downward strokes/
- Slant: Do letters slant to the left or right? You may be able to use a protractor to determine the degree of the slant.
- Baseline habits: Does the author write on the line or does the writing go above or below the line?
- Fancy writing habits: Are there any unusual curls or loops or unique styles?
- Placement of diacritics. How does the author cross the t's or dot the i's?
- Develop the Fingerprints. Hold up the bag from the crime scene with the fingerprints. Put 3 or 4 drops of Krazy Glue on a small piece of aluminum foil. Place the glue so that it won't directly touch the cup and seal the bag and put it some place safe. Explain that over several hours, the gas from the glue will adhere to the oils of the fingerprints and make the fingerprints appear white and easier to see. Explain that you will have them try to identify the fingerprints the next time you meet.
(Note: You can do your own DNA fingerprinting lab if you can buy Edvotek Kit #109 ($79), electrophoresis apparatus ($199), power supply ($199), automatic micropipet and tips ($179), balance, microwave or hot plate, white light visualization system ($119). Obviously this is out of most home educator's budget for just one science demonstration. I felt I needed to say, however, that it can be done at home, if you are so inclined.)