Ana Alicea Diaz, 1 M.F.S.; Alan F. Boehm, 1 M.F.S.; and
Walter F. Rowe, 1 Ph.D.
Comparison of Fingernail Ridge Patterns of
REFERENCE: Diaz, A. A., Boehm, A. F., and Rowe, W. F., "Comparison of Fingernail
Ridge Patterns of Monozygotie Twins," Journal of Forensic Sciences, JFSCA, Vol. 35, No.
1, Jan. 1990, pp. 97-102.
ABSTRACT: The ridge patterns on the fingernails of corresponding fingers of a pair of twins
were compared microscopically and found to be readily distinguishable from one another.
Based on blood grouping in six blood group systems (ABO, Rhesus, Ss, Duffy, Kidd, and
Kell), the probability that the twins were monozygotic was calculated to be 89.1%.
KEYWORDS: forensic science, fingernails, human identification, fingernail ridge patterns,
Over the years there has been interest in the use of fingernail ridge patterns as a means
of personal identification [1-9]. Such use requires that the fingernail ridge patterns ap-
pearing on a person's fingernails be unique. Both MacDonell and his colleagues [4--7]
and Haag  have reported comparisons of the fingernail ridge patterns on the fingernails
of monozygotic (identical) twins. In all of the reported twin studies, the fingernail ridge
patterns on the corresponding fingers of each twin did not match. None of these studies
offered any genetic evidence that the twins studied were in fact monozygotic. Haag relied
upon the self-description of the twins he studied. Medical researchers have found a
classification error of 2 to 5% when twins are asked to classify themselves . MacDonell
 also presented a variety of anthropometric measurements of one set of twins that he
studied. While such measurements are highly suggestive that the twins studied were in
fact monozygotic, most of these measurements do not lend themselves to a calculation
of the probability that the twins were actually dizygotic. We present here the results of
a study in which the fingernail ridge patterns of a pair of twins whose red blood cells had
been grouped in six blood group systems were compared microscopically.
Materials and Methods
The subjects of this study were a pair of 48-year-old black, female twins (hereafter
designated J. A. and J. D.), one of whom was hospitalized at Walter Reed Army Medical
Center, Washington, DC. Full-width fingernail clippings were obtained from each finger
of each twin using cosmetic fingernail clippers. Each clipping was initially taped to a
labelled index card and placed in an envelope. Each clipping was subsequently mounted
Received for publication 5 Jan. 1989; accepted for publication 23 Jan. 1989.
~Graduate students and associate professor, respectively, Department of Forensic Sciences, The
George Washington University, Washington. DC.
Copyright © 1990 by ASTM International
98 JOURNAL OF FORENSIC SCIENCES
on a metal specimen stub and sputter-coated with an approximately 0.15-nm layer of
gold and palladium using a Samsputter-2a sputter coater (Touimis Research Corp., Rock-
ville, Maryland). Such coating renders the fingernail clippings opaque and facilitates their
subsequence microscopic examination. The coated clippings were compared microscop-
ically with an American Optical Corp. UFM-2 forensic microscope (Model K2031A)
equipped with x 1.2, • 2, and x 4 objectives and a fiber optic illuminator. Photomicro-
graphs were made with Polaroid 665 positive/negative black-and-white film.
Blood samples were taken from each twin by medical personnel at Walter Reed Army
Medical Center and typed in the ABO, Rhesus, Ss, Duffy, Kidd, and Kell blood group
Results and Discussion
The results of the blood typing of the twins are given in Table 1. Each twin had the
same blood type in each of the blood group systems. The probability that the twins were
in fact dizygotic was calculated from these blood grouping results using the methods of
Maynard-Smith and Penrose . The result is shown in Table 2. The probability that
the twins were in fact dizygotic was found to be 10.9%; therefore, the probability that
the twins were monozygotic was 89.1%. In these probability calculations, the initial
TABLE 1--Blood grouping results for a pair of twins
(J. A. and J. D.).
System J.A. J.D.
Fy(a - b - )
Jk(a + b + )
Fy(a - b - )
Jk(a + b + )
aMost probable genotype R~R0.
TABLE 2--Probability of dizygosity based on genetic and other data.
Initial probability of dizygosity
Probability based on likeness of sex
Probability based on likeness of ABO type
Probability based on likeness of Rhesus type
Probability based on likeness of Ss type
Probability based on likeness of Duffy type
Probability based on likeness of Kidd type
Probability based on likeness of Kell type
Total relative probability of dizygosity, pD
Total probability of dizygosity, pO/(1 + pD)
"Based on a frequency of 71.092% for black dizygotic twins ,
DIAZ ET AL. ?9 COMPARISON OF FINGERNAIL RIDGE PATTERNS OF TWINS 99
probability of dizygosity was based on a rate of dizygotic twins in the U.S. black population
of 71.092% . Gene frequencies for the U.S. black population published by the Amer-
ican Association of Blood Banks  were used in the remaining calculations.
The fingernail ridge patterns on the corresponding fingers of this pair of twins did not
match when they were compared microscopically. Figures 1 through 3 show photo-
micrographs of the fingernail clippings from the left index, left ring, and right middle
fingers, respectively. Clearly, these ridge patterns are readily distinguishable from one
another. These results give further indication that fingernail ridge patterns are unique
and consequently may be used for personal identification.
The ridge patterns appearing on the fingernails of a pair of twins were compared
microscopically and found to be readily distinguishable. Based on blood grouping in six
blood group systems (ABO, Rhesus, Ss, Duffy, Kidd, and Kell), the probability that the
twins were monozygotic was calculated to be 89.1%.
FIG. 1--Photomicrographs of fingernail clippings from left index fingers of twins J. A. (upper)
and J. D. (lower).
JOURNAL OF FORENSIC SCIENCES
FIG. 2--Photomicrographs of fingernail clippings from left ring fngers of twins J. A. (upper) and
J. D. (lower).
DIAZ ET AL. ?9 COMPARISON OF FINGERNAIL RIDGE PATTERNS OF TWINS
FIG. 3--Photomicrographs of fingernail clippings from right middle fingers of twins J. A. (upper)
and J. D. (lower).
102 JOURNAL OF FORENSIC SCIENCES
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Address requests for reprints or additional information to
Walter F. Rowe, Ph.D.
Department of Forensic Sciences
The George Washington University
2036 H St., NW
Washington, DC 20052