Abstract

Objective

In this science project, you'll collect, categorize, and compare the fingerprints of siblings versus unrelated pairs of individuals to determine if fingerprint patterns are inherited.

Introduction

During weeks 10 through 24 of gestation, ridges are formed on the epidermis, which is the outermost layer of skin, on your fingertips. The pattern that these ridges make is known as your fingerprint. 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.

The three fingerprint patterns are illustrated here (FBI website).

The DNA they inherit from their parents determines many other personal characteristics and traits, like whether someone is right- or left-handed or the color of their eyes. In this project you'll 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.

Terms, Concepts, and Questions to Start Background Research

To do this science project, you should research the following terms and concepts:

• Gestation
• Epidermis
• DNA
• Fingerprint patterns
• Biological siblings
• Fingerprint formation
• Genetics
• Inheritance
• In utero

Questions

• What does it mean to be biologically related?
• What are fingerprints and how are they formed?
• What procedures do officials, like the police, use to record fingerprints?
• What are the different types or classes of fingerprints?

Bibliography

• The FBI website describes how to take fingerprints.
  FBI. (n.d.). Taking Legible Fingerprints. Federal Bureau of Investigations, Criminal Justice Information Services. Retrieved February 12, 2008 from http://www.fbi.gov/hq/cjisd/takingfps.html
• This Australian police website describes fingerprints, how they're formed, and their uses in forensics.
  Lennard, C. and Patterson, T. (2003). Dactyloscopy: The Science of Fingerprinting. New South Wales Police Service. Retrieved February 12, 2008 from http://www.policensw.com/info/fingerprints/indexfinger.html
• This Wikipedia entry gives an overview of fingerprints and their history.
  Wikipedia contributors. (2006). Fingerprints. Wikipedia, The Free Encyclopedia. Retrieved February 12, 2008 from http://en.wikipedia.org/w/index.php?title=Fingerprint&oldid=190845125

Materials and Equipment

Before starting this science project, you should gather together these items:

• Black ink pad
• White paper
• Paper towel
• Moist towelettes for cleaning hands (cotton balls dipped in rubbing alcohol will also work)
• Magnifying glass

Experimental Procedure

1. To start this science project, practice taking reliable clear fingerprints. Ask a friend or family member to let you learn by using his or her fingers.
   1. Use a moist towelette to clean the person's right index finger.
   2. Thoroughly dry the finger with a paper towel.
   3. Roll the right index finger on a black ink pad.
   4. Then roll the inked finger onto white paper using light but constant pressure.
   5. Use another towlette to clean the person's inked finger.
   6. Perfect your technique until fingerprints come out clear each time.
2. Make up a consent form for your project. Because fingerprints can be used to identify people, you'll need their consent to take and use their fingerprints.
3. Take fingerprints of pairs of siblings and of pairs of unrelated people.
   1. Make sure they sign a consent form BEFORE you take the fingerprint.
   2. Use the cleaning and inking system you developed to take the fingerprint of each person's right index finger.
   3. Label each fingerprint with a unique code, which will tell you which pair the fingerprint belongs to and whether that is a sibling pair or an unrelated pair. An example of an appropriate code would be to give each pair a number and each individual a letter. Siblings would be labeled as subjects A and B while unrelated individuals would be labeled as subjects D and Z. Thus, fingerprints from a sibling pair might carry the codes 10A and 10B while fingerprints from a unrelated pair might be labeled 11D and 11Z.
   4. Collect fingerprints from at least 15 sibling pairs and 15 unrelated pairs. For unrelated pairs, you can actually use sibling 1A with sibling 2B since these individuals are not related to each other. The more pairs you look at in your science project, the stronger your conclusions will be! For a more in-depth look at how the number of participants affects the reliability of your conclusions, see: "Sample Size: How Many Survey Participants Do I Need" at http://www.sciencebuddies.org/science-fair-projects/project_ideas/Soc_participants.shtml.
4. Examine each fingerprint using your magnifying glass and characterize it as a whorl, arch, or loop pattern. Fill out a data sheet like the one below.

   Related Pairs (unique ID)	Fingerprint Category (arch/whorl/loop)	Category match? (yes/no)
   10A
   10B
   Unrelated Pairs (unique ID)	Fingerprint Category (arch/whorl/loop)	Category match? (yes/no)
   11D
   11Z

5. Compare the percentage of related pairs whose fingerprint patterns match to the percentage of unrelated pairs whose fingerprint patterns match.
   1. Are they the same? Which is higher?
   2. What does this tell us about whether fingerprints are genetic?
   3. Identical twins share 100% of their DNA. Does your data include any identical twins? Do they have the same fingerprint pattern?

Variations

• How do your results change if you compare all 10 fingers, rather than just 1? Do all 10 fingers from the same person have the same fingerprint?
• Toes also have ridge patterns. Do "toe prints" follow the same rules as fingerprints?
• Are some patterns more common than others?
• If you make more quantitative measurements of the fingerprint patterns, can they be used to predict sibling pairs? With what degree of accuracy?
• If fingerprints are unique, why do misidentifications occur in forensics? How easy or hard is it to match a fingerprint with an individual?
• Read about statistics and use a mathematical test (like Fisher's exact test) to determine if your findings are statistically relevant. To do this, you'll need to make sure you understand p values and you'll need to think about whether your sample size is large enough. Online calculators, like the one from GraphPad Software, are good resources for this analysis.

• For more science project ideas in this area of science, see Genetics & Genomics Project Ideas.

Credits

Sandra Slutz, PhD, Science Buddies

Last edit date: 2008-02-21 14:00:00