Working with Canine Chromosomes: Current
Recommendations for Karyotype Description
N. Reimann, S. Bartnitzke, I. Nolte, and J. Bullerdiek
There is an increasing interest in genomic research on the domestic dog (Canis
familiaris). However, these investigations are complicated by the canine karyotype
comprising 76 acrocentric autosomes of similar size and shape and the metacentric
sex chromosomes. None of the numerous published ideograms and karyotypes
has yet been generally accepted. The present article gives a review of these descriptions of the canine karyotype. The two most recent nomenclatures and the
current efforts toward a standardized canine karyotype made by the Committee for
the Standardized Karyotype of the Dog are discussed in detail and recommendations for future use of a nomenclature for the canine karyotype are given.
From the Center for Human Genetics and Genetic Counselling, University of Bremen, Leobener Str. ZHG, D28359 Bremen, Germany (Reimann, Bartnitzke, and Bullerdiek) and the Clinic for Small Animals, School of Veterinary Medicine, Hannover, Germany ( Nolte). This
work was supported by a grant from the Deutsche Forschungsgemeinschaft. Address correspondence to Dr.
J. Bullerdiek at the address above. This paper was delivered at the International Workshop on Canine Genetics at the College of Veterinary Medicine, Cornell
University, Ithaca, New York, July 12–13, 1997.
q 1999 The American Genetic Association 90:31–34
Many of the genetic diseases, including
cancer, known to occur in dogs (Canis familiaris) are counterparts of human genetic
diseases. Comparative approaches aimed
at the characterization of genetic diseases,
gene mapping, and gene therapy have
much to offer for the benefit of both dogs
and humans. Thus there has been an increasing interest in genomic research on
the dog. International projects aimed at
producing a high-quality genetic map for
the dog genome have been established
( Dog Genome Project, DogMap). However,
this research is complicated by the dog
karyotype. The canine karyotype is one of
the most difficult karyotypes among the
mammalian species. It consists of 76 acrocentric autosomes which are all similar
in size and shape and the metacentric X
and Y chromosome. The largest autosome
is almost equal in length to the X chromosome and the Y chromosome is the
shortest of the complement. A standardized nomenclature for the complete canine karyotype comparable to that of the
human karyotype ( ISCN 1995) or the standard systems of the karyotypes of laboratory mice (Committee on Standardized
Genetic Nomenclature for Mice 1972), laboratory rats (Committee for a Standardized Karyotype of Rattus norvegicus 1973),
and cattle, sheep, and goat ( ISCNDA 1989)
does not yet exist.
Description of the Canine
Karyotype: A Historical Review
During the last 100 years several reports
about the description of the karyotypic
pattern of the dog have been published. In
the very early reports the diploid number
ranged from 50 to 78 (Ahmed 1941; Minouchi 1927; Painter 1925; Rath 1894). Because of the development of new technologies ( hypotonic treatment of the cultured cells; Hsu and Pomerat 1953) a diploid chromosome number of 78 was
determined for Canis familiaris (Chiarelli
1966; Gustavsson 1964; Hare et al. 1965).
Further development of various chromosomal banding techniques led to a more
precise description of the canine karyotype. Table 1 summarizes the published
ideograms for the canine G-banded chromosomes. The first description of the Gbanding pattern was published by Selden
et al. (1975). In this report an ideogram
with 331 G bands per haploid set was established. One year later Manolache et al.
(1976) presented a schematic representation with 230 G bands and a different arrangement of the chromosomes. Moreover, they described the Q- and C-banding
pattern of the canine karyotype. The next
ideogram for canine G-banded chromosomes was proposed by Fujinaga et al.
(1989). In this ideogram the arrangement
of the chromosomes followed Manolache
et al. (1976) and the number of G bands
per haploid set was 228. This report included the N-banding pattern of the karyotype of the dog. A further ideogram for
canine chromosomes was produced by
Stone et al. (1991) using a cell synchronization technique. In their schematic representation 327 bands were given, while
the arrangement of the chromosomes fol-
31
Table 1. Published ideograms for canine G-banded chromosomes
Author (year)
Number of bands
per haploid set
Chromosome arrangement
according to
Additional information
Selden et al. (1975)
Manolache et al. (1976)
331
230
Fujinaga et al. (1989)
228
Manolache et al. (1976)
Stone et al. (1991)
327
Selden et al. (1975)
Graphodatsky et al. (1995) 460
Reimann et al. (1996)
460
Selden et al. (1975)
Switonski et al. (1996)
235 for 21 chromosome
pairs 1X1Y
Selden et al. (1975)
lowed Selden et al. (1975). Graphodatsky
et al. (1995) were the next to publish an
ideogram. In this report 460 bands were
numbered and characteristic landmarks
were described. The alignment of the
chromosomes followed none of the previous reports.
In addition, ideograms for R-banded
chromosomes have repeatedly been described as well, each with different chromosome arrangements and numbers of
bands ( Howard-Peebles and Pryor 1980;
Poulson et al. 1990). In summary, none of
the published ideograms has been generally accepted. Two very recent proposals
are described in detail below and recommendations concerning their future application are given.
Q banding
C banding
Q banding
C banding
N banding
Q banding
C banding
NOR banding
Landmarks
Numbered bands
Centromere position
Landmarks
Numbered bands
G and R banding comparison
Landmarks
Numbered bands
An Extended Nomenclature of the
Canine Karyotype
A major disadvantage of the published
ideograms and karyotypes was that the
problem of the orientation of the acrocentric chromosomes was not solved. Moreover, most of the proposed ideograms
were initially deduced from more than one
karyotype (Graphodatsky et al. 1995; Selden et al. 1975). Consequently, the relative
sizes of the chromosomes do not fit each
other. In addition, in all reports a comparison between G and R bands is missing. In
1996 we published a study in which we
tried to overcome these problems (Reimann et al. 1996a). A combined GTG-banding/fluorescence in situ hybridization
( FISH) approach using an alpha-satellite
probe specific for canine chromosomes
( Fanning 1989) resulted in the detection of
positive signals in all canine autosomes allowing us to determine the centromere position of each canine chromosome ( Figure
1). With this approach we not only solved
the problem of the correct orientation of
the autosomes, but we also detected polymorphisms for the centromeric regions of
chromosome 12 and 37. The centromeric
regions of both sex chromosomes were
lacking signals with the same molecular
probe, leading us to conclude that the centromeric alphoid regions of the sex chromosomes differ widely from those of the
autosomes in the canine karyotype.
For our proposed ideogram, no synchronization procedures or other techniques
to obtain high-resolution chromosomes
were applied. Cytogenetic investigations
of fibroblasts of a female mixed breed revealed the best results in terms of band
resolution and one of these metaphases
( Figure 2) was basically used for our ideogram with 34 characteristic landmarks and
460 numbered bands in order to maintain
the correct size relations of the chromosomes. We arranged our chromosomes according to Selden et al. (1975), because it
is the most commonly used nomenclature
for the canine karyotype thus also facilitating the comparison between past, present, and future cytogenetic investigations
in dogs. Figure 3 shows a comparison of
the ideogram by Selden et al. (1975) and
Figure 1. Results of the combined GTG-banding/FISH approach with an alpha satellite probe specific for canine chromosomes: (a) prebanded GTG-banded metaphase; (b)
same metaphase after FISH.
32 The Journal of Heredity 1999:90(1)
Figure 2. Karyogram of the canine GTG-banded metaphase which was used as the basis for the proposed ideogram. To complete the karyotype a Y chromosome was taken from a different metaphase.
our schematic representation of the canine chromosomes. The ideogram was
overchecked by comparing its banding
pattern with several metaphases from different dogs. In previous studies we have
analyzed more than 1000 metaphases from
100 different dogs (e.g., Bartnitzke et al.
1992a,b; Reimann et al. 1994, 1996b).
Our study also provides a direct comparison between GTG bands and RBG
bands on canine chromosomes. Not unexpectedly, when comparing two sets of
karyotypes, differences in chromosome
morphology and banding patterns are obvious. Nevertheless, the correspondence
of the two banding patterns is approximately 80%, thus enabling the use of the
same arrangement of the chromosomes,
regardless of whether R or G bands have
been demonstrated.
Committee for the Standardized
Karyotype of the Dog
During the 11th European Colloqium on
Cytogenetics of Domestic Animals, held in
Copenhagen, Denmark, in 1994, the Committee for the Standardized Karyotype of
the Dog, with members from six different
laboratories, was established. The first approach of this group was to perform a
comparison test aimed at the question
how many chromosome pairs could be
recognized unequivocally with the use of
G-banding techniques on mid-metaphase
chromosomes. For this purpose, each laboratory sent one metaphase to the other
laboratories, where it was karyotyped.
The results allowed standardization of Gband patterns of the first 21 autosomes
and the sex chromosomes (Switonski et
al. 1996). It was foreseen that the identification of the remaining 17 autosome pairs
based on this resolution of bands would
require the integration of molecular cytogenetic methods. Only just recently, chromosome paints specific for canine chromosomes were developed by Langford et
al. (1996). In their report the paints for the
first 21 autosomes and the sex chromosomes were assigned according to the
Standard Committee, for the remaining 17
autosome pairs the assignment was still
missing. It was decided that the assignment of the paints to these chromosomes
should be carried out by the members of
the Standard Committee, thus integrating
the paints into the standardization procedure. Therefore, during the second stage
of the standardization of the canine karyotype, combined banding/FISH studies
with chromosome paints were carried out
by the different laboratories of the committee. The results of these investigations
led to assignment of the remaining paints.
The identified chromosomes 22–38 were
arranged according to Selden et al. (1975).
As for the description of characteristic
landmarks and numbered bands, it was
decided to adapt the ideogram described
by Reimann et al. (1996a). A report about
the results of the second stage of the Standard Committee for the Canine Karyotype
is in preparation.
Conclusion
Figure 3. Comparison between the schematic representation for canine chromosomes by Selden et al. (1975)
( left) and by Reimann et al. (1996a) (middle). The chromosomes on the right side derived from the karyotype
shown in Figure 2.
There is an increasing interest in working
with canine chromosomes. On the one
hand there are the international projects
( Dog Genome Project, DogMap) which include physical gene mapping, and on the
other hand there are scientists analyzing
the genetic background of canine diseases
and cancer. However, these studies have
been complicated by the rather difficult
situation concerning the description of
the canine karyotype. The aim of this report is to prevent this confusion. Thus, depending on the type of study and the resolution of bands on the chromosomes, basically two nomenclatures should be used
in the future: the one described by the
Standard Committee, and the one described by Reimann et al. (1996a).
When working with mid-metaphase
Reimann et al • Working with Canine Chromosomes 33
chromosomes it is recommended that the
nomenclature of the Standard Committee
be used. However, in these cases the application of FISH with the painting probes
specific for canine chromosomes will be
essential for the identification of the smaller autosome pairs (chromosomes 22–38).
A description of landmarks and bands for
the small chromosomes of these metaphases is lacking from the Standard Committee. Studies dealing with chromosomes
showing a higher resolution of bands, for
example, tumor cytogenetic investigations
and gene mapping studies, should refer to
the nomenclature of Reimann et al.
(1996a). These recommendations are supported by the Standard Committee.
Recommendations concerning the use
of a nomenclature for the description of
chromosomal aberrations in the canine
karyotype have not yet been made. We
recommend that in these cases the ISCN
(1995) should be used as a reference.
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Corresponding Editor: Gregory M. Acland