Forensic Science

DNA testingForensic Science and DNA

As they sift through the aftermath of a crime, forensic scientists might long for some solid DNA samples, a videotape of the crime, or even a piece of clothing, but they have to work with whatever evidence they can find. Often, that means height and foot size or fingerprints.  Here’s how they investigate.

Fingerprint investigation

FingerprintFor over 100 years, police agencies have had a powerful tool in combating crime. The use of fingerprinting allows crime fighters an extremely accurate means of identification. Other means of identification (such as hair colour or style, weight, or eye colour) may change, but fingerprints do not.

The patterns of ridges on our finger pads are unique: no two individuals, even identical twins, have fingerprints that are exactly alike. We leave impressions, or prints, of these patterns on everything we touch with any pressure.Injuries such as burns or scrapes will not change the ridge structure: when new skin grows in, the same pattern will come back.

Fingerprints differ from person to person based upon distinctive patterns of ridges. There are seven different finger print patterns used for identification purposes.
•    Central Pocket Loop Whorl
•    Double Loop Whorl
•    Accidental Whorl
•    Plain Arch
•    Plain Whorl
•    Right Slant Loop
•    Left Slant Loop
•    Tented Arch

Fact: Dactyloscopy is the practice of using fingerprints to identify someone.

How can they be identified when found at a crime scene?

One way that detectives locate fingerprints is by dusting for them. Fingerprints are coated with powder, then lifted and taken for identification at the lab. Try your hand at being a detective by dusting for fingerprints.
You will need these materials:
•    Drinking glass
•    Cocoa
•    Small soft brush (soft camel hair or fiberglass)
•    Transparent tape
•    5 sheets of light-coloured construction paper

Dusting a Glass

1. When fingers are oily or sticky you get better fingerprints.  So press an oily or sticky finger on the side of a drinking glass.
2. Coat the fingerprints with a dusting of cocoa powder.
3. Brush gently with either a camelhair or fiberglass brush. The fingerprints remain.
4. Place the sticky side of the tape on the dusted fingerprint. Lift on the tape and place on light colored construction paper. Talcum powder should be used on dark surfaces.

Try this out! Your feet can predict your height

The bones of the feet can tell a lot about a person. What do feet reveal about a person's height? When a forensic scientist has the length of a foot, they will be able to approximate the height of the individual. This works best on a full grown individual for the ratio of body parts is slightly different in growing children.
Steps to create a spreadsheet that determines height and foot length
1. Create a spreadsheet. List the individuals name, height, and foot length.
2. Have some adults remove their shoes and measure their height.
3. Measure the length of the adult's left foot from the wall to the tip of the big toe.
4. Examine the numbers. Do you see a pattern?
5. Divide the length of each person's left foot by his/her height. Multiply the quotient by 100. What do you get? You may also want to use the calculator for this activity.
6. The results of your calculations should be about 15, illustrating that the length of a person's foot is approximately 15 percent of his or her height.
7. Find out the approximate height of each of your classmates by measuring their foot and charting it on a spreadsheet. Use this proportion for your calculations: 15/100 = Length of foot divided by that person’s height.

What is DNA?


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