Fingerprints are static and do not change with age, so an individual will have the same fingerprint from infancy to adulthood. The pattern changes size, but not shape, as the person grows. (To get a better idea of how that works, you can model the change in size by inking your fingerprint onto a balloon and then blowing up the balloon.) Since each person has unique fingerprints that do not change over time, they can be used for identification. For example, police use fingerprints to determine whether a particular individual has been at a crime scene. Although the exact number, shape, and spacing of the ridges changes from person to person, fingerprints can be sorted into three general categories based on their pattern type: loop, arch, and whorl, as shown in Figure 2, below.

      
Figure 2. The three basic fingerprint patterns are illustrated here. (Image credits: FBI website)

The DNA that a person inherits from their parents determines many personal characteristics and traits, like whether someone is right- or left-handed or the color of their eyes. In this science project, you will examine fingerprints from siblings versus pairs of unrelated individuals to figure out if general fingerprint patterns are genetic or random. Have you ever looked at two girls and said, “you must be sisters”? We can often tell that two people are siblings because they appear to have several similar physical traits. This is because children receive half their DNA from each parent. All biological siblings are the mixture of both parents’ DNA. This results in a greater degree of matching traits between siblings than between unrelated individuals. Therefore, if DNA determines fingerprint patterns, then siblings are more likely to share the same fingerprint category than two unrelated individuals are.

INQUIRY: Study fingerprints like a Forensic scientist

To study fingerprints, you’ll need:

• white paper
• clear tape
• a pencil
• a magnifying glass

Step 1: Trace your hands on white paper, using a pencil.

Step 2: On a different piece of paper, scribble hard with pencil until a small area is covered with graphite. Rub your left pinkie around in the graphite until it is covered with gray.

Step 3: Carefully place your left pinky finger on the sticky side of a piece of clear tape, then gently lift your finger off of the tape. A clear fingerprint should be visible.

Step 4: Place the tape face-down on the left pinky finger of each of their traced hand.

Step 5: Repeat this with each finger of your left hand until you have fingerprints on each of the five fingers traced. Now do it with their right hands.

Repeat step 6 with your parents and siblings

Step 6: Examine each fingerprint and characterize it as a whorl, arch, or loop pattern. Use a magnifying glass if you have it.

What pattern do you observe? Are the patterns similar to your parents and siblings. Make a chart to better compare the results.