It’s All In the Genes: A classroom study on polygenic
inheritance.
Intended for Grade: 7th grade science
Subject: Science
Description:
For many traits in humans, the genetic traits may be controlled by many genes. These
traits may be quantitative in value which include size, shape, weight, height, skin color,
eye color and finger ridge patterns (TRC). Typically, polygenic traits have a continuous
distribution in a population and the distribution closely represents a bell-shaped curve or
normal distribution. Additionally, individuals are affected by environmental factors, and
the phenotype is determined by the sum of all the active alleles present in the individual.
This activity will analyze the total finger ridge patterns of your class to determine
whether it follows a typical normal distribution.
The total ridge count for a particular finger is obtained by joining the points from the
center of the pattern to the triradius (triradii, if more than one) and counting the ridges
crossed by this line. A triradius is a point at which three groups of ridges, coming from
three directions, meet at angles of about 120 degrees. The Total Ridge Count (TRC) is
the sum of the ridge count for the 10 fingers. The pattern type and ridge count are useful
in studying variability in human populations because of their objectivity and stability
after the fourth fetal month and high genetic component. The average TRC for males is
145 and that for females is 126. For an arch, the ridge count is 0.
Objective:
Students will analyze the total finger ridge patterns (TRC) in class to determine whether
it follows a typical binomial distribution, which is a characteristic of traits controlled by
the additive effect of many genes (polygenic inheritance). Also, students will study basic
DNA structure and gene regulation.
Background Material:
The following website can provide background material for classroom discussion:
http://biology.kenyon.edu/courses/biol114/Chap01/Chapter_01b.htm
NSF North Mississippi GK-8
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Mississippi State Frameworks Addressed:
7th Grade Science:
2a Distinguish genes as sections of DNA molecules that carry the genetic code for
inherited traits.
7th Grade Math:
4b.
Interpret and construct histograms, line, and bar graphs.
4e.
Estimate and compare data including mean, median, mode, and range of a set of
data.
National Frameworks Addressed:
Content Standard C, Life Science
Math Standard, Data Analysis and Probability
Materials:
1. 8 x 11 white paper
2. ink pad
3. Dissecting Microscope or magnifying glass (optional)
4. Baby wipes
5. a pencil
NSF North Mississippi GK-8
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How to count ridges:
The ridge count on a finger with a loop pattern is determined by counting the
number of ridges between the triradius and the center of the pattern. The whorl
pattern count is determined by counting the distance from each triradius and
using the higher of the two as the ridge count. The ridge count for an arch
pattern is 0.
Procedure:
1. Carefully roll each finger back and forth on the ink pad. Make sure that the triradius of
each finger is smeared on the ink pad, shade a 3cm x 3 cm square on piece of paper. This
is very important!!!! If the triradius cannot be identified, it is difficult to determine the
fingerprint pattern.
2. Gently press and roll each finger on the score sheet. A baby wipe can be used to
remove ink smears from each finger.
3. Classify your fingerprints as having a looped, arched, or whorled pattern and record
the data. A dissecting microscope or magnifying glass may be used to assist in
determining fingerprint patterns. When classifying looped and whorled fingerprint
patterns, mark the triradius with a pencil and count from the triradius to the center (core)
of the fingerprint.
4. A summary of data from the class will be compiled to compare the average ridge
counts between males and female.
5. Carefully place the first phalange of your index finger on the graphite area. Make sure
the triradius of your finger is well smeared with the black graphite.
http://www.usask.ca/biology/211blab/Lab7/POLY.html
NSF North Mississippi GK-8
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SCORE SHEET:TOTAL RIDGE COUNT
Right Hand
TRC
Left Hand
TRC
Sub
totals
Thumb
Thumb
_____
_____
First finger
_____
First finger
_____
Second finger
_____
Second finger
_____
Third finger
_____
Third finger
_____
Fourth finger
_____
Fourth finger
_____
NSF North Mississippi GK-8
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Keywords:
DNA
polygenic inheritance
fingerprint patterns
alleles
normal distribution
mean
mode
Data Table
Total ridge count (individual): _________
Total ridge count (females)_________
Total ridge count (males)___________
Total ridge count (class)________
Calculations:
1. Calculate your total ridge count. _______
2. Calculate the range for your individual total ridge count._______
3. Calculate the mode for your individual total ridge count.________
4. Calculate the mean for male total ridge count in the class._________
5. Calculate the range for male total ridge count in the class._______
NSF North Mississippi GK-8
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6. Calculate the mode for male total ridge count in the class.________
7. Calculate the mean for female total ridge count in the class._________
8. Calculate the range for female total ridge count in the class._______
9. Calculate the mode for female total ridge count in the class.________
10. Calculate the mean for the class data._________
11. Calculate the range for the class data.______
12. Calculate the mode for the class data.______
13. How does your individual TRC compare to the TRC for the class?____males?_______- females?________
Take home assignment:
Students must construct a line or bar graph illustrating the total ridge count of males and
females in the class.
Prepared by:
Michael D. Smith
Fall 2004
NSF NMGK-8
University of Mississipp
NSF North Mississippi GK-8
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