Vol. 56, no. 4: 375-385, 2003
CARYOLOGIA
Review
Chromosome polymorphism and karyotype
evolution of four canids: the dog, red fox, arctic fox
and raccoon dog
M. SWITONSKI*, N. ROGALSKA-NIZNIK, I. SZCZERBAL and M. BAER
Department of Genetics and Animal Breeding, August Cieszkowski Agricultural University of Poznan, Wolynska 33, 60-637
Poznan, Poland.
Abstract - In the family Canidae a wide range of the diploid chromosome numbers is observed, from 34 + B in the red fox to 78 in the dog and the wolf. Moreover, extensive chromosome polymorphisms were described in some species. In
the red fox and raccoon dog a variable number of B chromosomes exist, while
in the arctic fox such variability is caused by the widely spread Robertsonian
translocation. Also size polymorphism of heterochromatic arms appears in the
arctic fox. During the last ten years very rapid progress has been achieved in the
mapping of the dog genome and it has facilitated the construction of genome
maps of other canids, as well. The application of the comparative chromosome
painting approach and the analysis of the chromosome localisation of marker loci
have facilitated detailed studies on chromosome rearrangements which occurred
during the karyotype evolution. It is foreseen that the extended knowledge on the
canine genome organisation will be useful not only in the detection of gene
mutations causing hereditary diseases in the dog, but also will facilitate the identification of genes responsible for the great phenotypic and behavioural variability
of the dog breeds. Potentially this knowledge may also be useful in fur animal
breeding.
Key words: family Canidae, comparative cytogenetics, karyotype evolution,
chromosome polymorphism, B chromosomes, heterochromatin, genome map,
dog, red fox, arctic fox, raccoon dog.
The family Canidae consists of 36 species
(WAYNE and VILA 2001), among which there are
the dog and three livestock species, namely the
arctic fox, red fox and raccoon dog, which are
kept in captivity on fur-animal farms. In this family a wide range of the diploid chromosome number is observed, from 34 + variable number of B
chromosomes in the red fox to 78 in the dog and
wolf (W AYNE 1993). Interestingly, the intraspecies variability of the diploid number of chromosomes exists in the arctic fox, red fox, and
* Corresponding author: fax +48 61 8487148; e-mail:
[email protected]
raccoon dog. These features were extensively
studied by cytogeneticists in the 1970s and 80s.
In the beginning of the 1990-ties, genome
mapping of domestic animals became a very
important approach in genetic studies. At present, a comprehensive canine marker genome
map covers all chromosomes and includes information on 3270 genetic markers (GUYON et al.
2003). Rapid progress in this field has facilitated
comparative genome analysis, including evolution studies of some species belonging to this
family. The analysis of the mammalian genome
evolution, with the use of the comparative chromosome painting, made it possible to reconstruct
376
the ancestral karyotype of the order Carnivora,
which consisted of 42 chromosomes, and most of
them are also conserved in the cat karyotype, but
are highly rearranged in the dogs (YANG et al.
2000; MURPHY et al. 2001).
The aim of the present paper is to review the
knowledge on chromosome polymorphism and
the evolution of four species belonging to the
family Canidae: the dog, red fox, arctic fox and
raccoon dog. These four species represent four
genera, out of the fifteen known in the family
Canidae.
Inter- and intraspecies variability of the diploid
chromosome numbers
The highest diploid number of chromosomes
(2n=78) in the family Canidae is found in the dog
(Canis familiaris) and its ancestor - the wolf (Canis lupus). In the karyotype of this species all autosomes are one-armed (acrocentric), while both
sex chromosomes are bi-armed. The X chromosome is a large metacentric chromosome and the
Y chromosome, the smallest element in the karyotype, is metacentric as well (SELDEN et al. 1975).
The karyotype of the dog is very stable and no
polymorphism concerning the number and structure of chromosomes was observed. Since the
recognition of small autosomes is very difficult,
only a partial G-banded standard karyotype,
comprising 21 biggest autosome pairs and the
sex chromosomes, was published (SWITONSKI et
al. 1996a). However, the application of chromosome specific painting probes and locus-specific
probes facilitated the distinguishing of all homologous chromosome pairs (BREEN et al. 1999).
In the arctic fox (Alopex lagopus) the basic
diploid chromosome number is 50. The majority
of autosomes are bi-armed and only two pairs
are acrocentrics. The X chromosome is metacentric and the Y is an acrocentric. The standard Gbanded karyotype for the arctic fox was developed by MÄKINEN et al. (1985a). Extensive chromosome polymorphism, caused by the Robertsonian translocation between the only two acrocentric autosomes - No. 23 and 24, is found in
this species. Thus, three karyotype forms are present with diploid chromosome numbers: 50, 49
and 48 (GUSTAVSSON and SUNDT 1967). The distribution of these karyotype forms was analyzed
on fur animal farms in Poland, Czechoslovakia,
Denmark, Sweden and Finland (table 1). In general, the most frequent (44.4%) form appeared to
be heterozygous for the translocation (2n=49);
SWITONSKI, ROGALSKA-NIZNIK, SZCZERBAL
and BAER
however, quite a wide variability occurred
between populations. The effect of this polymorphism on fertility was also studied. Surprisingly, almost in all the reports increased fecundity of females homozygous for the translocation
was observed (CHRISTENSEN and PEDERSEN 1982;
MÄKINEN and LOHI 1987; FILISTOWICZ et al.
2001). A lack of the negative effect on the fertility of animals having 49 chromosomes could be
explained by the observation of meiotic chromosome pairing. The application of the synaptonemal complex technique in an electron microscope
revealed the presence of a regular trivalent in the
spermatocytes of heterozygous males. An abnormal pairing behavior, i.e. the association between
the X-Y bivalent and the trivalent, was observed
rarely (SWITONSKI and GUSTAVSSON 1991).
The raccoon dog (Nyctereutes procyonoides) is
recognised as the oldest member of the family
Canidae and represents a separate branch on the
phylogenetic tree with the divergence from other
canids dating at least 7-10 million years ago
(WAYNE 1993). In the karyotype of the raccoon
dog many segments homologous to chromosomes
of the predicted ancestral karyotype for the order
Carnivora were identified. Thus, it has been suggested that the raccoon dog has the most primitive karyotype in the Canidae family (WAYNE et
al. 1987). There are two subspecies distinguished:
the Chinese raccoon dog Nyctereutes procyonoides procyonoides (N.p.p.) and the Japanese
raccoon dog Nyctereutes procyonoides viverrinus
(N.p.v.). The karyotype of the Chinese raccoon
dog (2n=54+B) is composed of five pairs of
biarmed autosomes and 21 pairs of acrocentric
autosomes. The sex chromosomes are also
biarmed - a medium-sized X and the Y being the
smallest chromosome in the karyotype. In addition, a variable (1-4) number of B chromosomes
exists in this karyotype (MÄKINEN et al. 1986). A
proposal of the chromosome nomenclature for
the Chinese raccoon dog was recently presented
by PIENKOWSKA et al. (2002). The Japanese raccoon dog karyotype (2n=38+B) comprises 13
pairs of biarmed chromosomes, 5 pairs of acrocentric chromosomes and biarmed X and Y
chromosomes. In this subspecies a variable number (2-7) of B chromosome is also present (WADA
and IMAI 1991; WADA et al. 1998). In spite of
the fact that karyotypes of both subspecies differ
in the chromosome number and morphology,
they share the same fundamental number of chromosome arms - 66 (MÄKINEN et al.1986).
377
CHROMOSOME POLYMORPHISM AND KARYOTYPE EVOLUTION IN CANIDS
In the silver fox (Vulpes vulpes) the diploid
chromosome number is 34 plus B chromosomes
(0-8). It is the lowest diploid chromosome number found in the family Canidae (WURSTER and
BENIRSCHKE 1968). The karyotype consists of biarmed autosomes only. The X chromosome is a
metacentric and the Y is an acrocentric. The standard karyotype of this species was established by
MÄKINEN et al. (1985b).
TAVSSON and SUNDT 1967). This suggestion was
recently supported by comparative chromosome
painting (YANG et al., 1999). The B chromosomes of the red fox are C-band negative and it
is in contrast to the same sized Y chromosome,
which has a distinct CBG positive centromere
region. Inheritance studies of the B chromosomes in the silver fox showed that their segregation to gametes is non-mendelian in character
and so they are transmitted randomly to progeny (SWITONSKI 1984).
In the raccoon dog quite large acrocentric B
chromosomes occur. They differ in size in the
two subspecies. In the Chinese raccoon dog they
are medium-sized acrocentrics and in the Japanese raccoon dog they are small acrocentrics. The
Bs are rather C-band positive; however, the Cbanding patterns are not as distinct as in centromeres of the autosomes. The R-banding
showed that these structures are late replicating
(WURSTER-HILL et al. 1986).
A detailed molecular characterisation of the B
chromosomes was performed with the use of fluorescence in situ hybridisation (FISH). The application of the telomeric DNA probe revealed
hybridisation signals along the length of the raccoon dog B chromosomes. Thus, it was suggested that in both subspecies of the raccoon dog the
Bs are rich in telomeric or telomeric-like
sequences. In the same study it was shown that
the Bs in the red fox have only typical distal signals while hybridised with the telomeric probe
Nature of the B chromosomes
The diploid chromosome number variability
in the silver fox and the raccoon dog is caused by
the presence of the supernumerary B chromosomes. The occurrence of these structures is rare
in mammals. It should be emphasised that the
size and nature of B chromosomes in the both
species (the red fox and the raccoon dog) differ
significantly from each other. The B chromosomes of the red fox are very small and comparable in size to the Y chromosome. Their number varies from 0 to 8, but the most common
numbers are 2 or 3 (ELLENTON and B ASRUR
1981). A comparison of the B chromosome distributions in the populations of farm silver foxes (silver fox is a coat colour variant of the red
fox) and wild red foxes showed that in the red
foxes higher numbers of the Bs are observed Fig. 1 (SWITONSKI 1988). It was suggested that B
chromosomes in the red fox are evolutionary
remnants of the centric fragments derived from
the Robertsonian translocation events (G US-
50
wild
farm
40
%
30
20
10
0
0
1
2
3
4
5
6
Modal number of B chromosomes
Fig. 1 – Distribution of the modal number of B chromosomes in farm silver fox (511 animals) and wild red fox (108 animals) populations (adopted from SWITONSKI 1988).
378
SWITONSKI, ROGALSKA-NIZNIK, SZCZERBAL
(W URSTER -H ILL et al. 1988). The use of the
rDNA probe (genes coding rRNA genes) onto
the Chinese raccoon dog chromosomes showed
hybridisation also on a large segment of the Bs,
apart from terminal signals on three autosome
pairs and the Y chromosome, which are known
to carry active NORs (nucleolar organizer
regions). It suggests that B chromosomes of the
Chinese raccoon dog contain numerous repeats
of the NOR-like sequences as well (SZCZERBAL
and SWITONSKI 2003). For the B chromosomes
of the Japanese raccoon dog chromosome panting probes were developed by the microdissection technique. Complete B chromosome samples and particular segments of them were
obtained and specific probes were derived. The
Bs were equally painted by each probe and no
signals on autosomes and sex chromosomes were
detected. Thus, it was concluded that the Bs are
homologous with each other, but not with the
basic set of chromosomes (T RIFONOV et al.
2002). On the other hand, the B chromosome
specific paint probes, derived from flow sorted
chromosomes of the red fox, hybridised to the
Bs, but also to the centromeric area of the majority of bi-armed chromosomes and interstitially on
4p and 5p chromosome arms (YANG et al. 1999).
These results show that B chromosomes of both
species evolved independently and the Bs of the
raccoon dog may arise from one initial B chromosome.
The meiotic behaviour of the Bs indicates that
they are homologous within a species. Depending
on the number of Bs, different pairing configurations – univalents, bivalents and multivalents –
were observed in the primary spermatocytes of
and BAER
the silver fox (Fig. 2, SWITONSKI et al. 1987). Similar observations were described in the Chinese
raccoon dog by SHI et al. (1988).
Size polymorphism of the constitutive heterochromatin
Karyotypes of the canids differ substantially
from one another in terms of the amount and
distribution of constitutive heterochromatin. The
minimal amount of heterochromatin is present in
the karyotype of the red fox. Distinct C-bands
were observed only in the centromere region of
three autosomal pairs and in the Y chromosome.
The other autosomes had only small positive
dots in these regions. The X chromosome had a
diffuse proximal C-band in the long arm (MÄKINEN et al. 1985b). The amount of constitutive
heterochromatin in the dog is also small when
compared to the other species of the family
Canidae (PATHAK et al. 1982). Darkly stained
centromeric C-bands were detected in a few
chromosome pairs and the others had lightly or
unstained centromere regions. In the Chinese
raccoon dog all autosomes, except for chromosome No. 3, had large blocks of the centromeric constitutive heterochromatin (MÄKINEN et al.
1986). The karyotype of the Japanese raccoon
dog presents an unequal distribution of the centromeric heterochromatin. Some of the autosomes have a small C-band block, but some have
a very distinct C-band in the centromere area.
C-banding patterns of the X chromosome are
very similar in the raccoon dog and in the dog.
Apart from centromeric heterochromatin, a diffuse interstitial C-band in the q arm is also present. The Y chromosome in both subspecies of
Fig. 2 – Pairing behaviour of five B chromosomes in a primary spermatocyte of the red fox – synaptonemal complexes observed in an electron microscope; bivalent (small arrow) and trivalent
(large arrow) are indicated. Bar 1 µm.
CHROMOSOME POLYMORPHISM AND KARYOTYPE EVOLUTION IN CANIDS
the raccoon dog has a paracentromeric C-band
on the q arm. The canine Y chromosome
demonstrates a darkly stained long arm (PATHAK
et al. 1982; WARD et al. 1987).
An exceptional situation is present in the karyotype of the arctic fox, where ten pairs of small
autosomes have entirely heterochromatic short
arms (MÄKINEN et al. 1985a). These arms are
polymorphic in size. Quite a common situation is
a lack of one of such arms and it causes the occurrence of an extra acrocentric chromosome
(SWITONSKI et al. 1996b). Size polymorphism of
heterochromatic arms has a continuous character,
as it was revealed by the analysis of synaptonemal
complexes at the pachytene substage of the meiotic prophase I (SWITONSKI and GUSTAVSSON
1991). Since some bivalents had unequal lateral
elements it was assumed that it was caused by the
unequal length of the heterochromatic arms. In
the arctic fox also supernumerary heterochromatic chromosomes were identified. Unfortunately, their origin and inheritance were not
explained (MOLLER et al. 1985; MÄKINEN et al.
1981).
Nucleolar Organiser Regions and variability of
their activity
The number of Nuclear Organiser Regions
(NORs) is characteristic for a karyotype. In the
family Canidae the highest number of NORs was
found in the arctic fox. In the karyotype of this
species there are six chromosome pairs bearing
NORs: 13, 15, 17, 18, 20 and 22. In the silver fox
there are three autosome pairs with NORs – 8, 9
and 13 (MÄKINEN et al. 1985a and b). In the dog
and raccoon dog NORs residue on three autosome pairs and on the Y chromosome. The following chromosome pairs of these species bear
the NORs: 1, 4, 13 and Y in the Chinese raccoon
dog (PIENKOWSKA and ZAGALSKA 2001) and 11,
12, 18 and Y in the Japanese raccoon dog (WARD
et al. 1987). The NORs in the canine karyotype
were detected on two large autosomes (7 and
17), one small autosome and on the Y chromosome (MÄKINEN et al. 1997; PIENKOWSKA and
SWITONSKI 1998). The presence of the NOR on
the Y chromosome reflects the evolutionary similarity of this chromosome in the dog and raccoon dog.
The analysis of the NOR activity, studied by
silver staining, showed that the number of silver
deposits is somehow related to the number of
chromosomes bearing the NORs. In the dog, rac-
379
coon dog and red fox a modal number of active
NORs was five or six, while in the arctic fox it
was seven or eight. The NOR localised on the Y
chromosome appeared to be active in approx.
80% of chromosome spreads in both species, the
dog and the raccoon dog (PIENKOWSKA and
ZAGALSKA 2001).
Karyotype evolution
A comparison of the canid karyotypes, carried out with the use of the G-banding technique,
revealed a high homology between the dog and
both fox species, and an extensive whole arm
homology could be observed between the foxes
(GRAPHODATSKY et al. 1995; YOSHIDA et al. 1983;
MÄKINEN and GUSTAVSSON 1982). This high
homology of chromosome arms is also shared by
the foxes and the raccoon dog, since approximately 75% of chromosome arms of both foxes
have homologous counterparts in the raccoon
dog karyotype (WAYNE et al.1987). In the karyotypes of the Japanese raccoon dog and the Chinese raccoon dog chromosome arm homologies
were also studied by the comparison of banding
patterns (WARD et al. 1987). Despite the difference in the chromosome number, the G-banding
technique revealed extensive homology. These
results lead some authors to a conclusion that
the ancestral canid karyotype was dog-like and
that the centric and tandem fusions played the
main role in the karyotype evolution in this family (Y OSHIDA et al. 1983; W ARD et al. 1987;
GRAPHODATSKY et al. 1995). On the other hand,
TODD (1970) proposed that the ancestral karyotype was similar to that of the Japanese raccoon
dog and the karyotypes with higher diploid numbers evolved by centric fission events. This suggestion was supported by WAYNE et al. (1987)
who identified numerous homologous chromosome segments in the raccoon dog karyotype and
predicted the karyotype of the common canid
ancestor.
The application of the reciprocal chromosome
painting to compare karyotypes of some canids
and other species belonging to the order Carnivora showed that the ancestral Carnivore karyotype had a low diploid number (2n=42), with
mostly bi-armed chromosomes (MURPHY et al.
2001; GRAPHODATSKY et al. 2001; NASH et al.
2001). This novel cytogenetic technique did not
resolve questions concerning karyotype evolution of the canids. Two different diploid chromosome numbers in the ancestral canid kary-
380
otype were proposed. NASH et al. (2001) suggested that the canid ancestor karyotype evolved
from the carnivore karyotype mainly by the centric fission mechanism and finally had a dog/wolflike karyotype with a high diploid number of
one-armed chromosomes. Further, karyotypes of
other canids with low diploid numbers and a
SWITONSKI, ROGALSKA-NIZNIK, SZCZERBAL
and BAER
variable proportion of bi-armed chromosomes
evolved by extensive centric fusion events. In
contrary, GRAPHODATSKY et al. (2001) proposed
that the ancestral canid karyotype, which was
closely related to the ancestral karyotype of the
order Carnivora, had a low diploid number of biarmed chromosomes, and thus karyotypes of pre-
Fig. 3 – Possible mechanisms of karyotype evolution of four species belonging to the family Canidae: (a) modified from
GRAPHODATSKY et al. (2001), (b) modified from NASH et al. (2001).
381
CHROMOSOME POLYMORPHISM AND KARYOTYPE EVOLUTION IN CANIDS
Table 1 – Distribution of the karyotype polymorphic forms in populations of the arctic fox
N
Population (reference)
2n=48
9.7
25.2
17.5
26.2
14.3
34.1
25.4
18.8
10.6
20.2
Karyotype forms (%)
2n=49
2n=50
40.2
50.0
47.9
26.9
53.1
29.4
47.3
26.5
45.2
40.5
40.7
25.2
48.1
26.5
38.8
42.4
38.2
51.2
44.4
35.4
Sweden (MÄKINEN and GUSTAVSSON 1980)
Poland (SWITONSKI 1981)
Denmark (CHRISTENSEN and PEDERSEN 1982)
Norway (MOLLER et al. 1985)
Denmark (CHRISTIANSEN et al. 1986)
Poland (JASZCZAK et al. 1987)
Finland (MÄKINEN and LOHI 1987)
Czechoslovakia (PARKANYI et al. 1988)
Poland (FILISTOWICZ et al. 2001)
Total
82
401
135
1094
842
138
476
80
285
3533
sent-day canids evolved mainly by centric fissions
to high-diploid chromosome karyotypes (dog,
wolf) or by extensive reciprocal chromosome
translocations to low-diploid chromosome karyotypes (e.g. the red fox) and the amplification of
repetitive sequences (e.g. the arctic fox). Mechanisms describing the two alternative hypotheses
are shown on Fig. 3. It should be mentioned that
the karyotype of the Chinese raccoon dog was not
studied by the comparative chromosome painting
and thus its position on the tree is tentative.
Comparison of the cytogenetic marker genome maps
An advanced canine marker genome map is
widely applied to identify gene mutations responsible for hereditary diseases and cancer development. Nowadays, a few dozen of monogenic diseases were characterized on the molecular level
Table 2 – Cytogenetic (FISH) localisation of the canine-derived genetic marker probes
Canine marker probes
ZuBeCa2
ZuBeCa4
5SrDNA
ZuBeCa6
ZuBeCa35
ZuBeCa3, ZuBeCa12,
ZuBeCa13, ZuBeCa20, K9
ZuBeCa18
ZuBeCa36
ZuBeCa1
ZuBeCa17
LEP
IGF-I
ZuBeCa25,
ZuBeCa30,
ZuBeCa23
ZuBeCa7, ZuBeCa16,
ZuBeCa11,
ZuBeCa29
ZuBeCa5, ZuBeCa8
CanBern1
ZuBeCa21
ZuBeCa15
ZuBeCa9
ZuBeCa31
ZuBeCa26
K2e
ZuBeCa10
CanBern6
ZuBeCa28
Dog
1q (a)
3q (a)
4q (f)
Red fox
1p (a)
14q (a)
4q (f)
5q (a)
(b)
9q (a)
(e)
(a)
(b)
10q (a)
12q (a)
14q (i)
15q (i)
17q (a)
(b)
(a)
18q (a)
12q (a)
(b)
2p (a)
(e)
(a)
(b)
16q (a)
1q (a)
7q(i)
10q (i)
8q (a)
(b)
(a)
5q (a)
(b)
19q (a)
(b)
5p (a)
21q(a)
24q (a)
25q (a)
(b)
29q(a)
27q (e)
30q (a)
11p(a)
14p(a)
15q (a)
(b)
8p(a)
8p (e)
1q (a)
37q (b)
12q (b)
Chromosome
Arctic fox
2q (d)
4q (c)
3q (f)
10q (h)
(h)
12q (d)
(e)
(h)
Chinese raccoon dog
7q (d)
6q (h)
8q (f)
5q (d)
1q (d)
13q(i)
23q (i)
5p (d)
3q (d)
(g)
5q (d)
(e)
(g)
(h)
4q (d)
14q (d)
1p(i)
18q (i)
13q (d)
(h)
11q (d)
(c)
(d)
24q (d)
(c)
15q(h)
18q(h)
2p (d)
(h)
17q(h)
17q (e)
1q (d)
(g)
10p (d)
(h)
17q (d)
(h)
(d)
9q (d)
(h)
20q(h)
4p(g)
2q (d)
(h)
3p(g)
3p (e)
14q (d)
(h)
15q (d)
(a) YANG et al. 2000; (b) DOLF et al. 2000; (c) ROGALSKA-NIZNIK et al. 2000; (d) ROGALSKA-NIZNIK et al. 2003; (e) SZAMALEK et al.
2002; (f) PIENKOWSKA et al. 2002; (g) SZCZERBAL et al. 2003a; (h) SZCZERBAL et al. 2003b; (i) SZCZERBAL et al. 2003c.
382
and thus DNA tests are available to detect carriers of the mutated genes (PATTERSON 2000). In
the dog genome, among 3270 identified markers,
at least 300 microsatellite markers and 80 genes
have been physically mapped to the dog chromosomes (YANG et al. 2000; BREEN at al. 2001a
and b). It was shown that class I (genes) and class
II (microsatellites) genetic markers derived from
the dog genome may also be successfully used in
the physical mapping of the red fox (YANG et al.
2000), arctic fox and raccoon dog (ROGALSKANIZNIK et al. 2003; SZCZERBAL et al. 2003b). So
far, about 70 genetic markers have been assigned
to the red fox chromosomes by FISH and somatic cell hybridisation approach (SEROV and RUBSTOV 1998; YANG et al. 2000). The arctic fox and
Chinese raccoon dog genome maps are rather
poorly developed when compared with the red
fox one. Altogether 35 genetic markers were
chromosomally assigned in both the arctic fox
and Chinese raccoon dog genomes (ROGALSKANIZNIK et al. 2000, 2003; SZAMALEK et al. 2002;
PIENKOWSKA et al. 2002; SZCZERBAL et al. 2003a,
b, c). A comparative localisation of these loci is
given in Table 1.
The results of the physical mapping of the
arctic fox genome are in agreement with the
report on comparative chromosome maps of
the dog, red fox and the arctic fox genomes
(GRAPHODATSKY et al. 2000). It is however foreseen that extensive physical mapping of the fox
and raccoon dog genomes may reveal small intrachromosomal rearrangements which could not
be detected by comparative chromosome painting. An interesting example, given by ROGALSKANIZNIK et al. (2003), concerns the dog chromosome 9 (CFA9), the Chinese raccoon dog 5
(NPP5) and the arctic fox chromosome 12
(ALA12). The ALA 12q is painted by the CFA9
whole chromosome painting probe. The obtained
results suggest that a fragment of the NPP5q was
inverted in the ALA12q. The centromere position
of the canine CFA9 has been conserved according to the Chinese raccoon dog chromosome, but
it is orientated towards the telomeric region of
the ALA 12. Moreover, three closely localised
microsatellites on the NPP5q (ZuBeCa12, ZuBeCa13 and ZuBeCa20) residue on two different
fragments of the CFA9 and ALA12. The
rearranged order of the loci (ZuBeCa25 and
ZuBeCa30) was also observed on the CFA17 and
ALA5p when compared with the NPP13. This
also was probably caused by an inversion.
SWITONSKI, ROGALSKA-NIZNIK, SZCZERBAL
and BAER
Conclusions and perspectives
The introduction of comparative chromosome
painting to studies on karyotype evolution
brought new data on chromosome rearrangements which occurred during the process of speciation. Detailed studies were carried out on
species belonging to four families: Canidae
(YANG et al. 1999, 2000; GRAPHODATSKY et al.
2001; TRIFONOV et al. 2002), Mustelidae (NIE et
al. 2002), Ursidae (NASH et al. 1998) and Felidae
(WIENBERG et al. 1997) of the order Carnivora.
Cytogenetic studies of species belonging to the
family Canidae have revealed exceptional differences between their karyotypes. A wide range of
the diploid chromosome numbers, the presence
of the B chromosomes in the fox species, the
localization of the Nucleolar Organizer Regions
on the Y chromosome in the dog and the raccoon
dog, and a great variability of the constitutive
heterochromatin content reflect dynamic changes
which have occurred in the course of karyotype
evolution. This situation is rather unique in the
order Carnivora, especially when compared with
a very static karyotype in the family Felidae. In
spite of quite extensive studies on chromosome
polymorphism in the fox species and the raccoon
dog, there are still issues which are poorly understood: (a) what is the effect of large amounts of
constitutive heterochromatin in the arctic fox?
(b) what mechanism controls the number of the
B chromosomes in the red fox and raccoon dog?
(c) is there any effect of the B chromosomes number variability?
The application of molecular techniques in
genetic studies of the dog resulted in the development of advanced cytogenetic and linkage
genome maps. Reciprocal comparative chromosome painting revealed a high rate of homology
of chromosome arms in the karyotypes of the
studied species of the family Canidae. It can be
foreseen that the development of genome maps
of other canids and their comparison with the
canine map may bring new data concerning intrachromosomal rearrangements which took place
during evolution. On the other hand, the marker
genome map of the fox species and the raccoon
dog may potentially prove to be an important
tool useful in the identification of genes controlling traits important in fur animal breeding.
Acknowledgement - This study was supported
by the Foundation for Polish Science (contract
13/2000 and 76/2003).
CHROMOSOME POLYMORPHISM AND KARYOTYPE EVOLUTION IN CANIDS
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