Fingerprint Ridge Count A polygenic trait useful classroom instruction In Gordon Mendenhall Thomas Mertens Jon Hendrix Gordon Mendenhall teaches biology and human genetics at Lawrence Central High School, 7300East 56th St., Indianapolis, IN 46226. In 1986he received the Presidential Award for Excellencein Science Teaching and since 1984has been working with his co-au- thors in NSF-funded genetics and bioethics teacher education projects at Ball State University. Thomas Mertens and Jon Hen- drix are both professors of biology at Ball St¥e University, Muncie, IN 47306. Both men have been active in NABT, Mertens serving as president in 1985 and Hendrix as director-at-large in 1986and 1987. In teaching genetics, including human genetics, most instructors tend to emphasize single gene traits. Polygenic traits tend to be neglected in the classroom and laboratory despite the fact that in a variety of or- ganisms many significant traits are inherited in this manner. Basichuman genetics textbooks often cite as examples of traits that fit the polygenic model of in- heritance skin color, stature and intelligence as mea- sured by lQ tests. While these traits do exhibit the characteristics associated with polygenic inheritance, they are not easily illustrated with concrete examples in the typical classroom. The purpose of this paper is to describe how the polygenic trait of total fingerprint ridge count can be used in the classroom as a laboratory investigation. Student fingerprint data can be collected with ease and little expense. Teachers can exploit student in- terest in their own fingerprints and those of their peers to illustrate a model for polygenic inheritance. Background In 1890,Francis Galton suggested fingerprints as a useful tool in personal identification (Penrose 1969). Over the years, the patterns of epidermal ridges and flexion creases on the fingers, toes, palms of the hands and soles of the feet have become of interest to a variety of specialists. Dermatoglyphics, a term coined in 1926by Harold Cummins, is the study of the epidermal ridges; in practice it includes other aspects of hand, finger and foot prints (Penrose 1969). Fingerprints and other dermatoglyphic data can be obtained from newborns to support clinical diagnosis of chromosome abnormalities such as Down's syndrome. Although certain dermatoglyphic patterns may be associated with specific chromo- some aberrations, teachers should especially empha- size to their students that no single fingerprint pat- p '. tern or ridge count is in itself abnormal, While the formation of the epidermal ridge pattern and the total ridge count are polygenic, they are also influenced by environmental factors and thus may be said to be multifactorial (Penrose 1969). The embry- ology of the epidermal ridges offers clues to the pre- natal environmental influence on their pattern of de- velopment. Fetal fingertip pads are observable around the sixth week of gestation and reach their maximum size by week 12 or 13, after which they regress, giving rise to elevated dermal ridges (Moore 1987).The ridges, once formed, are very resistant to later prenatal or postnatal influences, thus making them an ideal trait for genetic studies as well as for identification of individuals. Classification of Fingerprints Fingerprint patterns of dermal ridges can be classi- fied into three major groups: arches, loops and whorls (see Figure 1). The arch is the simplest and least frequent pattern. It may be subclassified as "plain" when the ridges rise slightly over the middle of the finger or "tented" when the ridges rise to a p6int. The loop pattern has a triradius and a core. A triradius is a point at which three groups of ridges coming-from three directions meet at angles of about 120 degrees. The core is essentially a ridge that is surrounded by fields of ridges which turn back on themselves at 180degrees. Loops can be either radial or ulnar. A finger possesses a radial loop if its tri- radius is on the side of the little finger for the hand in question and the loop opens toward the thumb. A finger has an ulnar loop if its triradius is on the side of the thumb for that hand and the loop opens to- ward the little finger. The whorl pattern has two tri- radii with the ridges forming various patterns inside. FINGERPRINT 203
Transcript
Fingerprint RidgeCountA polygenic trait useful
classroom instruction
In
Gordon MendenhallThomas MertensJon Hendrix
Gordon Mendenhall teaches biology and human genetics atLawrence Central High School, 7300East 56th St., Indianapolis, IN46226. In 1986he received the Presidential Award for ExcellenceinScience Teaching and since 1984has been working with his co-au-thors in NSF-funded genetics and bioethics teacher educationprojects at Ball State University. Thomas Mertens and Jon Hen-drix are both professors of biology at Ball St¥e University,Muncie, IN 47306. Both men have been active in NABT, Mertensserving as president in 1985 and Hendrix as director-at-large in1986and 1987.
In teaching genetics, including human genetics,most instructors tend to emphasize single gene traits.Polygenic traits tend to be neglected in the classroomand laboratory despite the fact that in a variety of or-ganisms many significant traits are inherited in thismanner. Basichuman genetics textbooks often cite asexamples of traits that fit the polygenic model of in-heritance skin color, stature and intelligence as mea-sured by lQ tests. While these traits do exhibit thecharacteristics associated with polygenic inheritance,they are not easily illustrated with concrete examplesin the typical classroom.
The purpose of this paper is to describe how thepolygenic trait of total fingerprint ridge count can beused in the classroom as a laboratory investigation.Student fingerprint data can be collected with easeand little expense. Teachers can exploit student in-terest in their own fingerprints and those of theirpeers to illustrate a model for polygenic inheritance.
Background
In 1890,Francis Galton suggested fingerprints as auseful tool in personal identification (Penrose 1969).Over the years, the patterns of epidermal ridges andflexion creases on the fingers, toes, palms of thehands and soles of the feet have become of interest toa variety of specialists. Dermatoglyphics, a termcoined in 1926by Harold Cummins, is the study ofthe epidermal ridges; in practice it includes otheraspects of hand, finger and foot prints (Penrose1969). Fingerprints and other dermatoglyphic datacan be obtained from newborns to support clinicaldiagnosis of chromosome abnormalities such asDown's syndrome. Although certain dermatoglyphicpatterns may be associated with specific chromo-some aberrations, teachers should especially empha-size to their students that no single fingerprint pat-
p '.
tern or ridge count is in itself abnormal,While the formation of the epidermal ridge pattern
and the total ridge count are polygenic, they are alsoinfluenced by environmental factors and thus may besaid to be multifactorial (Penrose 1969). The embry-ology of the epidermal ridges offers clues to the pre-natal environmental influence on their pattern of de-velopment. Fetal fingertip pads are observablearound the sixth week of gestation and reach theirmaximum size by week 12 or 13, after which theyregress, giving rise to elevated dermal ridges (Moore1987).The ridges, once formed, are very resistant tolater prenatal or postnatal influences, thus makingthem an ideal trait for genetic studies as well as foridentification of individuals.
Classification of Fingerprints
Fingerprint patterns of dermal ridges can be classi-fied into three major groups: arches, loops andwhorls (see Figure 1). The arch is the simplest andleast frequent pattern. It may be subclassified as"plain" when the ridges rise slightly over the middleof the finger or "tented" when the ridges rise to ap6int. The loop pattern has a triradius and a core. Atriradius is a point at which three groups of ridgescoming-from three directions meet at angles of about120 degrees. The core is essentially a ridge that issurrounded by fields of ridges which turn back onthemselves at 180degrees. Loops can be either radialor ulnar. A finger possesses a radial loop if its tri-radius is on the side of the little finger for the hand inquestion and the loop opens toward the thumb. Afinger has an ulnar loop if its triradius is on the sideof the thumb for that hand and the loop opens to-ward the little finger. The whorl pattern has two tri-radii with the ridges forming various patterns inside.
FINGERPRINT 203
aFigure 1. Three principal types of fingerprint patterns: (a) arch with no triradius and a ridge count of 0; (b) loop with onetriradius and a ridge count of 12 and (c) whorl with two triradii and a ridge count of 15 (the higher of the two possiblecounts). [Reproduced with permission of the Biological Sciences Curriculum Study from Basic genetics: A human approach.(1983). Dubuque, IA: KendalVHunt Publishing Co.]
Ridge Count
The focus of this investigation is the polygenic traitcalled the total ridge count (TRC), the sum of theridge counts for all 10 fingers. Holt (1968) found thatthe average TRC for males is 145 and for females,126.
The ridge count on a finger with a loop is deter-mined by counting the number of ridges between thetriradius and the center or core of the pattern. For anarch, the ridge count is O.For a whorl a ridge count ismade from each triradius to the center of the finger-print, but only the higher of the two possible countsis used (Figure 1).
The Polygenic Inheritance Model
The inheritance of many significant human behav-ioral, anatomical and physiological characteristics isbest explained by a polygenic model of transmission.The inheritance of polygenic traits cannot be ana-lyzed by the pedigree method used for single genetraits, nor by chromosome studies as might be donein the case of suspected chromosomal anomalies.Polygenic traits, in contrast to single gene traits andchromosome abnormalities, exhibit a wide and con-tinuous range of expression and are measurable innature. Expression of polygenic traits is often mark-edly affected by the environment, causing them to bereferred to as multifactorial traits.
The assumptions underlying the polygenic modelof inheritance include the following (Nagle 1984):
• the trait is controlled by many independently as-sorting gene loci.
• each gene locus may be represented by an activeallele which contributes an increment or by aninactive allele that contributes no increment tothe phenotype.
• the alleles at each gene locus lack dominance,and each active allele has an effect on phenotypethat is small and equal to that of each of the otheractive alleles affecting the trait.
• phenotype is determined by the sum total of allthe active alleles present in the individual.
• finally, polygenes are not qualitatively differentfrom other genes-they regulate the productionof polypeptides and they segregate and indepen-dentiy assort according to Mendelian principles.
Any basic human genetics textbook can provide thereader with examples of how the model can be ap-plied to specific traits such as height or skin color.
Classroom Activities
ObjectivesWhat can students be expected to learn from the
activities proposed in this paper? Upon completionof the activities and after the associated instruction,students will be able to:
• use a pencil and Scotch Tape to construct a chartof their own fingerprints.
• classify fingerprints into arches, radial and ulnarloops, and whorls.
• determine the total ridge count for a full set offingerprints.
• construct a histogram using the class data of totalridge counts.
204 THE AMERICAN BIOLOGY TEACHER, VOLUME 51, NO.4, APRIL 1989
• discuss the characteristics of the polygenic inher-itance model and why polygenic traits are moredifficult to study than single gene traits.
• solve problems concerning TRC by using a four-gene model to explain the inheritance of humanfingerprint total ridge counts.
Materials neededThe materials required to obtain the fingerprints
are minimal: a no. 2 lead pencil, a sheet of paper anda role of %-inch Scotch brand Magic Tape. A handlens, magnifying glass, or dissecting microscope ishelpful for examining the fingerprints and countingridges.
ProceduresThe following set of instructions will provide stu-
dents with sufficient information to prepare their fin-gerprints, determine their individual total ridgecounts, collect class data on TRCand prepare a histo-gram of the class data .
• Using a no. 2 lead pencil, on a piece of papershade in a square having sides three centimetersin length.
• Rub one of your fingers on the graphite square,making certain you have covered all the triradiion the fingerprint. Now carefully place a piece ofScotch Tape onto your blackened finger so that
the tape comes in contact with the entire print.Make certain you include any triradii on theouter edges of the finger by rolling the fingerover the tape in one smooth motion. Peel awaythe tape and affix it to the appropriate place onyour record sheet (Table 1).
• Repeat this process, preparing a print of each ofyour 10 fingers.
• Examine each print carefully; if a print is incom-plete, prepare a new one. You may wish to use ahand lens, magnifying glass, or dissecting micro-scope to classify the pattern (arch, loop, orwhorl) and to determine the ridge count for eachprint.
• Record your fingerprint pattern data, total ridgecount and sex on the table On the chalkboard, asdirected by the instructor.
• Use the class data to answer the following ques-tions and to construct a histogram (see Figure 2)in which frequencies are plotted against totalridge count.
QuestionsUse the class data recorded on the chalkboard to
answer the following questions:
1. What is the average TRC for the class?2. What is the average TRC for the males in the
class? For the females?
Table 1. Format for data sheet for fingerprints. Adjust spacing to allow room for placing fingerprints at indicated locations.
RIGHT HAND
Thumb Second Third Fourth FifthPattern
Ridge CountTotal =
Place Printsin This Space:
LEFT HAND
Thumb Second Third Fourth FifthPattern
Ridge CountTotal =
Place Printsin This Space:
TRC -
FINGERPRINT 205
3. How does your TRC compare to the average forthe class? To the average for your sex?
4. Is there a difference between male and femaleaverage TRCs? What might account for this differ-ence? How do the class data compare to theaverages published by Holt (1968): 145 for malesand 126 for females?
5. In your own words, summarize and describe thehistogram you produced from the class data. Howdo the data collected by your class compare toFigure 2?
6. If you had collected TRC data from more people,do you think the histogram for this larger sampleof data would look different from the one youprepared? Explain.
A Sample of Data
Fingerprint data were collected from 36 biologyteachers participating in an NSF-funded workshop atBall State University in July 1988 (Figure 2). Theaverage TRC for the 19 males in the sample popula-tion was 149.2; for the females it was 129.6. Theseresults compare favorably with those reported byHolt (1968):145 for males and 126 for females.
The frequencies for the different fingerprint pat-terns for the 36 participants in the workshop alsocompared favorably with Holt's (1968)data from thegeneral population:
Figure 2. Total ridge counts for 36 participants in 1988 NSFproject at Ball State University. Graph prepared by RichardMenger.
206 THE AMERICAN BIOLOGY TEACHER, VOLUME 51, NO.4, APRIL 1989
Extend Your Understanding with AdditionalTRe Problems
Total fingerprint ridge count exemplifies a poly-genic inheritance pattern. Penrose (1969)and othershave suggested that a minimum of seven gene locicontribute to the TRC, but the model hypothesizedin the problems that follow is a four-locus model.Thus, AABBCCDD represents the genotype for max-imum ridge count and aabbccdd symbolizes the geno-type for the minimum ridge count. Assume that eachactive allele adds 30 ridges to the TRC and thathaving the genotype aabbccdd produces a baselineTRC of 40 for males and 20 for females.
1. Predict the TRC for each of the following geno-types:AABBCCDD male.AabbccDd female. _AaBBCcDD male. _aaBbCCDd female. _
2. Write the genotypes of parents who are heterozy-gous for all four genes. Write the genotype oftheir child who has the maximum number of ac-tive alleles possible.
a. What are the TRCs for the parents and their'child (assume the child is a female)?
b. Calculate the probability that these parentswould produce a child with the maximumnumber of active alleles.
If an AaBBCcdd male mates with an AaBbCCDD fe-male,
a. What is the maximum number of ridge-pro-ducing genes possible in one of their chil-dren?
b. What would be the TRC for this child if it is amale? A female?
c. If this child is a male, will he have a higher orlower TRC than the parent with the higherridge count?
d. What is the minimum number of ridge-pro-ducing genes possible in a child of thiscouple?
e. If this child were a female, would she have ahigher or lower TRC than the parent withthe lower ridge count? Explain.
4. If an AaBBCcdd male were to mate with anAABbCcDD female,
a. What would be the probability of producinga child with the maximum number of activealleles?
b. What would be the TRC for this child if itwere male? Female?
5. How would you expect your TRC to compare withthat of your parents? Your siblings? Your grand-parents?
6. In problems I, 2, 3 and 4 above, you made somepredictions of TRCsbased on the genotypes of theindividuals involved. Suppose we measured theTRCs for some people with those genotypes andfound the actual values to be different from thosepredicted by your calculations. How would youexplain these discrepancies?
7. Write a paragraph in which you discuss the ge-netic and environmental components of multifac-torial inheritance.
A1?r\ot.-i\ oj d-e-. r c, 1[",:,;C<1r~"'j r ~-:
I)61,.A.!"f\ 's ')7 Vl C\...Y O'r..--.Q { .
A P o» ' c i(?i ": ~ h0 nd ') ~~_.1
ReferencesHolt, S.B. (1968). The genetics of dermal ridges. Springfield,
IL: c.c. Thomas Publishers.Moore, L.A. (1987,January). Dermatoglyphics. Gene Pool, a
Resource Letter for Educators and Students. (pp. 1-4).Dayton, OH: Children's Medical Center.
Nagle, J.J. (1984). Heredity and human affairs (3rd ed.). St.Louis: Times Mirror/Mosby College Publishing.
Reed, T. (1981). Review: Dermatoglyphics in medicine-problems and use in suspected chromosome abnormali-ties. American Journal of Medical Genetics, 8, 411-429.
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