A webpage about Newfoundland dogs from Karin Butenhoff
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Eine wichtige Anmerkungung zuvor: Der nachstehende Artikel ist 1987 verfasst worden. Damals war der Unterschied zwischen weiss-schwarzem Neufundländer und Landseer noch nicht so klar umrissen wie zur heutigen Zeit. Nichtsdestotrotz können Sie sich bei der Erwähnung der Rasse Landseer ebenso den weiss-schwarzen Neufundländer hineindenken, denn der genetische Ablauf ist derselbe.
Genetica 80: 115-128, 1990.
© 1990 Kluwer Academic Publishers. Printed in Belgium.
The inheritance of the piebald spotting pattern and its variation in Holstein-Friesian cattle and in Landseer-Newfoundland dogs
H. Pape
Institut für Geophysik, Postfach 1253, D-3392 Clausthal-Zellerfeld, FRG
Received 10. 11. 1987 Accepted in revised form 23.9.1989
Abstract
The black and white spotting patterns of Landseer
dogs are divided into qualitatively recognizable phenotypic classes. Breeding
data were obtained from the Swiss Dog Stud Book (SHSB) and from
breeders' recent records. A plausible interpretation assumed qualitative
inheritance of the generally accepted piebald spotting gene sp1
with at least two
modifiers, s2 and s3. The modifier genes are regarded as
minor spotting genes and may be responsible for white markings in the
related Newfoundland breed which has been cross-bred with Landseers.
The proposed scheme of
polygenic inheritance can also be applied to the piebald spotting pattern
of Holstein-Friesian cattle, using breeding data from literature.
Introduction
White spotting is a common observed trait in birds
and mammals, especially in domesticated species. lf spotting is present, the
propagation, migration and differentiation of melanocytes has been
disturbed so that the white areas lack melanocytes. Whether melanoblasts,
the melanosome-free precursers of melanocytes, are present depends on
special circumstances. The table of genes in the laboratory mouse of Green
(1975) contains 18 loci with 36 genes causing white spots, white hairs or
complete white fur from deficient melanocytes. It seems hopeless to guess
homologies of spotting loci between different species purely on the basis of
the black and white ratio of phenotypic expression and the dominance
behaviour with respect to the normal gene.
Little (1957, 1958) explained recessive spotting in dogs with an allelic series:
| S | self coloured |
| si | Irish spotting (white head blaze, breast, paws and tail tip) |
| sp | piebald spotting (coloured plates, separated or confluent) |
| sw | extreme-white piebald spotting (colourplates reduced in size and number or even absent) |
This series has been established mainly on the assumption that the
well-investigated hooded series of the Norway rat should be present with
homologous genes in dogs. As the phenotypic variation of the four alleles
will be extremely wide due to the action of unspecified modifiers, Little
gave an explanation for each result of his reported matings, but there is
no evidence that, if we accept spadditional factors siand sw
existin the same series.
For the present, one should be cautious and confine oneself to the
postulation of a single mutation sp1for
piebald spotting at the locus S1. As
genetic analysis, including additional genes, is more the objective of
studies of qualitative than of quantitative inheritance, the qualitative
traits of spotting should be recognized. The key for this is the
characteristic pattern of each type of spotting. From the point of view of
pattern comparison, piebald spotting in dogs with its typical distribution
of coloured spots poorly fits the pattern of the hooded rat, whereas in
other cases there will exist comparable patterns in different species.
The pattern of piebald spotting in dogs and cattle
Fig. 1. Examples of piebald spotted phenotypes in Landseer dogs: above - dark (D) or 'Mantel' class, middle - medium (M) or 'Iarge spots' class, below - light (L) or 'restricted spots' class.
Fig. 2. Examples of piebald spotted
phenotypes in Holstein Friesian cattle: above - class D, middle - class M,
below - class L.
The piebald pattern is composed of solid spots
which may join one another. In every case where they form a border line
against white, the boundary is composed of convex arcs (Figs. 1 and 2).
From this shape it can be concluded that each spot has grown radially. In
piebald dogs, a postnatal progression of the solid areas can be observed.
This general property is common to a group of spotting patterns in contrast
to another group, to which belongs spotting in Nubian goats, where the
boundaries are convex with respect to the white areas, which result from a
degeneration of melanocytes. Consequently the amount of white area may increase
with age in such cases.
The
formation of isolated pigment centers represents a normal developmental
stage during embryonic ontogenesis, which leads to the selfcoloured
condition before birth. In the mouse fetus, Shaible (1963) determined two
medial and six pairs of lateral regions where melanoblasts converge. This
pattern resembles a so-called demixing pattern which appears in all fields
of nature, where a homogeneous phase separates into two different phases,
for instance when a solid phase crystallizes from a solution. In such a
process the first step is the formation of germs. That is important for a
clear understanding of piebald patterns, one cause of which is the
hindrance of germination, so that several pigment centers are omitted. The
distribution of pigment centers reveals a certain regularity, insofar as
they keep a special distance from their neighbours. That is why each germ
is surrounded by an aureole, which is infavourable for further germination.
For this reason the number of primary pigment centers is limited. In the white
areas of a piebald coat, a second generation of germs may occur at a later
stage resulting in 'ticking'.
The second step of pigment
spot formation is lateral growth. This process can also be hindered with
the result that the white areas between the spots remain partially
uncovered by the coloured , phase'. A common misunderstanding assumes that
the white areas are not invaded by melanoblasts in any case. Although there
is a deficiency of melanoblasts, this region may contain several of them
which become evident on secondary germ formation.
The germination of pigment centers and the
growth of spots influence each other. As germination is hindered near the
boundary of a plate, a larger number of germs than normal can be created if
growth is retarded. Ort the other hand, rapid growth may be combined with a
reduction of germ number. Usually, germination and growth are
simultaneously reduced in some way. Generally, the location of pigment
centers depends on the idiosyncrasies of each spotting pattern. Therefore
Allan's famous centers of retreat (Allan 1914), which describe the most
conservative spots for the whole range of variation of piebald patterns,
have no general meaning, but solely give an insight into special spotting
types.
The piebald pattern of Landseer dogs, which is
much the same as that of Holstein-Friesian cattle, will be described in
terms of germination and growth of spots. The variation reaches from almost
solid coloured phenotypes to nearly completely white phenotypes. Even in
the dark types, the lower parts of the legs are white with more extension
of white on the hind legs.
For all types of variation the anterior part of
the body, especially the head, reveals a relatively larger portion of
coloured area than the posterior part. In other words, the white areas
increase downwards and backwards. This recognition can be compared with the
migration path of melanoblasts, which originate from the neural crest
(Rawles, 1940, 1947). The distal parts of the limbs are farthest away from
the starting line of the process. It is also necessary to take into account
that embryonic development proceeds from the anterior part of the body.
Thus, the typical piebald pattern is caused by a normal beginning of the
pigmentation process, followed by reduced growing velocity of spots in
later stages. The darker and even the medium phenotypes possess all the
pigment centers of normal development. In the lighter types, simultaneously
with extreme reduction of spot growth velocity, the number of pigment
centers is restricted. The most conservative spots are one pair of head
spots and a caudal spot.
lf we compare the typical piebald pattern
of dogs with the hooded rat pattern, several differences are obvious, though even in the hooded rat the head region is the
darkest part of the body. The trunk of the hooded rat lacks the typical
plates of the piebald pattern and reveals a dorsal stripe in stead. The domin
ance relation ship s differ, as the heterozygous H+h is
clearly distinct from the homozygous self H+H+by
having white legs, whereas the sp1
allele can be regarded as a recessive with respect to S1.
White marks in the progeny of self x piebald matings may occur, but
this has to be explained by auxiliary spotting genes. lf one wants to look for
comparable spotting patterns, the hooded pattern resembles much more the
English-type spotting of rabbits, which is similar with respect to a dorsal
stripe and incomplete dominance, than the piebald spotting of dogs. Therefore
the hooded series should not be transferred to dog genetics. Another spotting
pattern is the Irish spotting (of dogs and not of rats in this context) which
is generally present or allowed in Basenjis, the Sennenhund' breeds from
Switzerland, Border Collies, Bull Terriers, Boston Terriers and Boxers. It is
characterized by the presence of a head blaze, a white breast spot, white
paws and a white tail tip. Although the same marks appear in the piebald
pattern, there is a principal difference which becomes clear if one compares
Irish spotting with piebald spotting of the same grade of darkness. For
instance the head blaze is much larger in the Irish type for the same
percentage of coloured area. In most cases the white portion is larger on the
forelegs than on the hind legs. In contrast to the piebald spotting, the
anterior part of the body is most affected by restriction of spots. This
indicates that the early part of pigmentation history is especially
influenced. In any case, the Irish pattern cannot be regarded as a moderate
piebald type pattern, produced by a `weaker' allele of the same series, but
acting in the same way. It seems to be more likely that there exists a quite
different, non allelic gene sin.
Inheritance of the piebald pattern variation
Definition of classes of spotting type
These studies have been made for a dog breed (Landseer) and a cattle
breed (Holstein-Friesian), which seem to have been selected for a typical
piebald pattern over a long period. The Landseer data were collected by the
breeder Mrs. Karin Brönnecke, who evaluated the Swiss Dog Stud Book (SHSB) up
to 1979 and breeders' recent litter records, consisting of schematic drawings
of the piebald pattern of puppies. The coloration of the ancestors is
documented by photographs. The total range of variation of the piebald
spotting has been divided into three classes (Figs. 1 and 2) which are more
qualitatively than quantitatively defined:
D = Dark = 'Mantel' class
All pigment centers have germinated and grown to such an extent that instead
of isolated spots, a continuous overcoat ('Mantel') covers the back and
sides. Only small marks and usually most of the legs have been left white.
M = Medium = 'large spots' class
All or nearly all pigment centers are developed, but growth has been
reduced in such a way that especially the sides bear several isolated spots.
L = Light = 'restricted spots' class
The number and the size of spots are severely restricted, usually to
the most conservative of the Allan's pigment centers, for instance a pair of
dark spots in the head region and a spot at the tail base. Instead of
ordinary first-order spots, a number of small spots of a second order
germination of melanoblast cumulation may be found on the back and sides.
These spots should not be counted as pigment centers.
Several investigations of the inheritance of the piebald pattern in Holstein-Friesian
cattle have used a similar three class division. The classifications of Lauprecht (1926a, b) and of Wiesch (1929)
are based on the development of pigment centers. Dunn, Schneider and Webb
(1923) measured the quotient of black and white present in the coat. Their
classes are defined as
| Dark | (0,70-0,95), |
| Medium | (0,25-0,699), |
| Light | (0-0,249), |
with per cent black in brackets. Although a
quantitative one, this division coincides more or less with the qualitative
ones above. This is not the case for the quantitative division of Pfähler
(1931), because his medium class covers a very small interval (0,46-0,65
per cent black). It is a pity that the data of his thorough studies in 'Höhenfleckvieh'
and Holstein-Friesian cattle could not be included in the present
calculations.
Hypothetical genotypes related to classes of piebald spotting types
In dogs
there is little doubt that Landseers are homozygous for sp1
which is the main spotting gene
of the piebald pattern. Heterozygotes S1+sp
1 seem to be
clearly distinguishable from the darkest piebald types and can be
classified as selfcoloured Newfoundlands together with the homozygous
S1+ S1+. The offspring of crosses
between homozygous Landseers and Newfoundlands are self-coloured with or
without white markings. Such markings could be independent of the existence
of a single sp1gene, as
small white spots are common in Newfoundlands even in populations which
never produce piebald offspring.
Even in
cattle, a clear cut division into selfcoloured breeds and piebald breeds is
possible. Therefore the author disagrees with Lauprecht (1926a, b) who
supposes that the HolsteinFriesian breed mainly consist of S1
+sp1heterozygous
individuals, which present the majority of the desired medium spotted type,
and the three genotypes S1+S1+,
S1+sp1, and sp1
sp1 overlapping
in their phenotypic variation due to external influences or modifier genes.
Wiesch (1929) accepts the genetic explanation of
Funquist and Boman (1923) and Funquist (1927), who established a
quantitative inheritance of the variation of head patterns of cattle
involving three gene pairs. Having shown that the head pattern types can be
correlated with the main spotting types, Wiesch takes over the same scheme,
which does not discriminate between major and minor spotting genes.
The hypothesis proposed here differs from previous
schemes by assuming that the main spotting gene is homozygous through the whole
breed.The phenotypic variation is attributed to two pairs of modifier
genes. The hypothetical mode of action of the genes can be described more
precisely: The homozygous piebald spotting factor sp1
does not influence the embryonic
germination of pigment centers, if it acts alone. The only visible effect
is a reduction of growth in the later stages of spot development.
The phenotypic
expression of the minor spotting genes in the absence of homozygous
sp1will not
be discussed here. Now we are interested in the effects of interaction of
several spotting genes. From the golden hamster (Robinson, 1975), the
rabbit (Robinson, 1958) and the pigeon (Hollander, 1983), we can learn that
the white spotting genes characteristically interact synergistically to produce
greater areas of white than would be expected on simple proportional action
(Robinson, 1975). The following assumption about the minor spotting genes
proved to give the best results for the evaluation of matings.
First, a recessive spotting gene s2 is proposed which alters the
piebald pattern from the 'Mantel' type to the 'large spots' type, if it is
homozygous in addition to sp1sp1.
Then, a second modifier s3is introduced, which seems to be recessive,
if it acts alone, but which becomes dominant, when interacting together
with sp1sp1
Even in the heterozygous condition, it is able to change the 'Mantel' type to the
'large spots' type.
The restriction of pigmentation is considerably enhanced, if
sp1sp1is supported by both modifiers,
namely s2in homozygous and s3
in heterozygous or homozygous
state. Not only is the growth of plates there greatly reduced, but also the
germination of pigment centers is hindered, which is typical for the 'restricted
spots' spotting type.
In all, we get nine genotypes, which are thought to compose the piebald
breeds under consideration. Each phenotypic class of spotting pattern
comprises more than one genotype according to the following synopsis:
| Genotypes | Phenotypes | |||
| sp1sp1 | S2+S2+ | S3+S3+ | 'Mantel' type | DARK |
| sp1sp1 | S2+s2 | S3+S3+ | ||
| sp1sp1 | s2s2 | S3+S3+ | 'large spots' type | MEDIUM |
| sp1sp1 | S2+S2+ | S3+s3 | ||
| sp1sp1 | S2+S2+ | s3s3 | ||
| sp1sp1 | S2+s2 | S3+s3 | ||
| sp1sp1 | S2+s2 | s3s3 | ||
| sp1sp1 | s2s2 | S3+s3 | 'restricted spots' type | LIGHT |
| sp1sp1 | s2s2 | s3s3 | ||
Results of crosses among classes of piebald spotting type
The breeding data were collected so that parents
and offspring were determined with respect to their phenotypic spotting
class. From the combination of two parental classes, six phenotypic matings
are possible. One data set was obtained for Landseers and the following
sets for Holstein-Friesian cattle: three populations, investigated by
Lauprecht (herd A, herd B and herd C), data from Dunn, Webb and Schneider
and data from Wiesch. Additionally all cattle data were combined and
treated as a single set.
On the basis of the hypothesis that attributes the
variation of spotting pattern to the action of two pairs of modifiers in
the previously described mode, the proportions of phenotypes in offspring
can be calculated for the reported matings.As each phenotype consists of
two or more genotypes, the results depend on the frequencies of genotypes.
Assuming Hardy-Weinberg equilibrium within the populations, the
probabilities of genotypes can be easily calculated from the frequencies of
alleles of each locus, S2/s2and S
3+/s3 in our case.
For
each of the six phenotypic matings the distribution of spotting types in
offspring was calculated, the frequencies of the modifier genes increasing from
10 to 90 per cent by steps of 10 per cent. By comparing the calculated
tables with the observed values, for each type of mating good agreement
could be found within a range of gene frequencies. As the two gefie
frequencies will be characteristic values of a closed population, in an
ideal case they should be independent of the type of mating. Therefore for
each population two favourable modifier frequencies, common for all mating
types, were chosen. With these. frequencies the agreement between observed
and calculated values was studied by applying the χ2 test to each mating type
(Tables 1-5). The probability P for a set of matings was calculated with a
combined sum and Fisher test (Koziol and Perlman, 1978).
Table 1. Results of crosses among Landseers of various spotting classes.
| Matings between spotting classes | Spotting classes of offspring | Observed values | Expected values for S2, S3 | Gene frequencies S2, S3 | χ2 | Probability P | |
|---|---|---|---|---|---|---|---|
| M x M | D | 4 | 3.9 | 0.5; 0.4 | 4.54 | 0.11 | |
| M | 31 | 35.7 | |||||
| L | 10 | 5.4 | |||||
| M x D | D | 5 | 4.7 | 0.5; 0.4 | 0.02 | 0.89 | |
| M | 11 | 11.0 | } 12.3 | ||||
| L | 1 | 1.3 | |||||
| M x L | D | 0 | 0.6 | } 8.0 | 0.5; 0.4 | 2.40 | 0.13 |
| M | 10 | 7.4 | |||||
| L | 2 | 4.0 | |||||
| D x L | D | 5 | 6.8 | 0.5; 0.4 | 1.36 | 0.51 | |
| M | 24 | 20.6 | |||||
| L | 7 | 8.6 | |||||
Table 2. Results of crosses among Holstein-Fresian cattle of various spotting classes. (combined data from Wiesch (1929), Dunn et al. (1923) and Lauprecht 1926)).
| Matings between spotting classes | Spotting classes of offspring | Observed values | Expected values for S2, S3 | Gene frequencies S2, S3 | χ2 | Probability P |
|---|---|---|---|---|---|---|
| M x M | D | 85 | 76.0 | 0.4; 0.5 | 1.42 | 0.49 |
| M | 401 | 404.4 | ||||
| L | 90 | 95.6 | ||||
| M x D | D | 108 | 97.9 | 0.4; 0.5 | 1.69 | 0.44 |
| M | 160 | 167.3 | ||||
| L | 20 | 22.8 | ||||
| M x L | D | 0 | 12.6 | 0.4; 0.5 | 3.07 | 0.22 |
| M | 122 | 121.2 | ||||
| L | 88 | 84.2 | ||||
| D x L | D | 10 | 9.2 | 0.4; 0.5 | 2.65 | 0.27 |
| M | 28 | 23.9 | ||||
| L | 6 | 11.0 |
Table 3. Results of crosses among Holstein-Fresian cattle of various spotting classes (data from Wiesch, 1929)..
| Matings between spotting classes | Spotting classes of offspring | Observed values | Expected values for S2, S3 | Gene frequencies S2, S3 | χ2 | Probability P | |
|---|---|---|---|---|---|---|---|
| M x M | D | 8 | 7.7 | 0.4; 0.4 | 0.58 | 0.75 | |
| M | 69 | 63 | |||||
| L | 7 | 7.0 | |||||
| M x D | D | 4 | 4.8 | 0.4; 0.4 | 0.18 | 0.68 | |
| M | 13 | 10.7 | } 12.2 | ||||
| L | 0 | 1.5 | |||||
| M x L | D | 0 | 1.3 | } 17.4 | 0.4; 0.4 | 4.82 | 0.03 |
| M | 23 | 16.1 | |||||
| L | 5 | 10.6 | |||||
Table 4. Results of crosses among Holstein-Fresian cattle of various spotting classes. (data from Dunn et al. (1923).
| Matings between spotting classes | Spotting classes of offspring | Observed values | Expected values for S2, S3 | Gene frequencies S2, S3 | χ2 | Probability P |
|---|---|---|---|---|---|---|
| M x M | D | 2 | 2.8 | 0.4; 0.5 | 2.22 | 0.34 |
| M | 13 | 14.7 | ||||
| L | 6 | 3.9 | ||||
| M x D | D | 20 | 14.3 | 0.4; 0.5 | 5.39 | 0.07 |
| M | 17 | 24.4 | ||||
| L | 5 | 3.3 | ||||
| M x L | D | 6 | 6.0 | 0.4; 0.5 | 2.14 | 0.35 |
| M | 19 | 15.7 | ||||
| L | 4 | 7.3 | ||||
| D x L | D | 2 | 2.9 | 0.4; 0.5 | 6.21 | 0.05 |
| M | 12 | 20.6 | ||||
| L | 23 | 14.3 | ||||
| D x D | D | 4 | 4.3 | 0.4; 0.5 | 0.15 | 0.70 |
| M | 1 | 0.7 | ||||
| L | 0 | 0 | ||||
| L x L | D | 0 | 0 | 0.4; 0.5 | 0.07 | 0.79 |
| M | 2 | 1.7 | ||||
| L | 13 | 13.3 |
Table 5. Results of crosses among Holstein-Fresian cattle of various spotting classes. (data from Lauprecht (1926), herd A, B and C.
| Matings between spotting classes | Herd | Spotting classes of offspring | Observed values | Expected values for S2, S3 | Gene frequencies S2, S3 | χ2 | Probability P |
|---|---|---|---|---|---|---|---|
| M x M | A | D | 49 | 37.6 | 0.4; 0.5 | 5.27 | 0.08 |
| M | 187 | 200.1 | |||||
| L | 49 | 47.3 | |||||
| M x M | B | D | 7 | 10.1 | 0.3; 0.4 | 1.21 | 0.5 |
| M | 73 | 72.2 | |||||
| L | 23 | 20.7 | |||||
| M x M | C | D | 19 | 13.8 | 0.5; 0.6 | 5.23 | 0.08 |
| M | 59 | 58.3 | |||||
| L | 5 | 10.5 | |||||
| M x D | A | D | 52 | 47.6 | 0.4; 0.5 | 1.90 | 0.40 |
| M | 81 | 81.6 | |||||
| L | 7 | 11.1 | |||||
| M x D | B | D | 3 | 5.3 | 0.3; 0.4 | 1.39 | 0.50 |
| M | 13 | 10.9 | |||||
| L | 2 | 1.8 | |||||
| M x D | C | D | 29 | 27.4 | 0.5; 0.6 | 1.50 | 0.47 |
| M | 36 | 39.8 | |||||
| L | 6 | 4.0 | |||||
| M x L | A | D | 2 | 5.0 | 0.4; 0.5 | 2.50 | 0.37 |
| M | 53 | 47.8 | |||||
| L | 31 | 33.2 | |||||
| M x L | B | D | 2 | 2.4 | 0.3; 0.4 | 0.15 | 0.93 |
| M | 32 | 30.7 | |||||
| L | 24 | 24.9 | |||||
| M x L | C | D | 2 | 0.7 | 0.5; 0.6 | 0.17 | 0.18 |
| M | 2 | 5.2 | |||||
| L | 5 | 3.1 |
Herd A P= 0.19
Herd B P= 0.84
Herd C P= 0.24
P values for the separate and combined test matings for all populations are high. That means the probability is high that the deviation of observed from calculated values is caused by random variation and not by a false hypothesis.
From the distributions of offspring phenotypes (which are not presented), calculated for the whole range of modifier frequencies, it appears that moderate variation of gene frequencies does not greatly affect the distribution values, whereas several attempts with other hypotheses led to quite different distributions, which could not be brought into an agreement with the observations.
In Landseers and in Holstein-Friesian cattle, the frequencies of the modifier genes s2 and s3 are each near to 50 per cent. Obviously, the piebald breeds with a desired 'large spots' pattern remain heterozygous with respect to minor spotting genes, although homozygous with respect to the piebald gene sp1. A comparison of the three herds A, B, C according to Lauprecht suggests the following: Herd A, with abundant 'large spots' phenotypes, has the modifier frequencies 0,6 s2 and 0,5 s3. These values are shifted to higher frequencies (0,7 s2 and 0,6 s3) for the herd B, which has been selected for light phenotypes. The opposite is true for herd C, which is rich in dark phenotypes, with a consequent decrease of modifiers (0,5 s2 and 0,4 s3). Nevertheless, this short term time selection in one or the other direction has not altered the mainly heterozygous condition of modifier genes.
According to the hypothesis, that matings M x M, D x M, M x L and D x L produce offspring distributed among the three clases. If the 'lage spots' pattern is desired, mating within this class and the compensating cross D x L give the best results. The matings D x D and L x L theoretically give offspring of the parental phenotype and of the medium class, but not of the opposite extreme class. This is in agreement with the observed data, as stated by Wiesch (1929). As the dark and light class contain one double homozygous genotype each, and the medium class two, it should be possible to establish pure breeding strains of each pattern. This would be a trouble-some task, involving a lot of test matings. If the two homozygous Iarge spots' pattern genotypes could be separated all efforts would have been for nothing when the two strains were mated together. Simple selection for the Iarge spots' pattern will achieve the heterozygous condition of minor spotting genes. Thus the present hypothesis offers an explanation for the vast variation in patterns, a peculiarity typical of piebald spotted breeds.
Inheritance of small white marks in dogs
Distinction between phenotypic classes in Newfoundlands
The breed closest related to the Landseer is the
Newfoundland. The origin of both breeds has been assumed to lie in the
Newfoundland region, where the dogs have been used for water work by
fishermen. When these dogs became famous, puppies were raised for export to
Europe, where pure breeding started. Study of stud books shows that
Landseers have been introduced into the Newfoundland breed and vice versa.
Nowadays breeders question whether this practice should be allowed or not.
One aspect is the fear of mismarking. Therefore the following study on
white marks in Newfoundlands has been carried out, assuming that the same
spotting genes are acting as in Landseers.
As a
first approximation, the common Newfoundland shall be regarded as the
selfcoloured and the Landseer as the piebald spotted variety of the same
breed. lf one looks very carefully at the coat of dark Newfoundlands,
sometimes one will find white marks. Thus, even Newfoundlands cover a range
of spotting grades including the absolutely self-coloured type.
Fortunately, there is a gap between the range of Landseer piebald patterns
and the range covered by Newfoundland phenotypes. In other breeds this gap
is occupied by the Irish type of spotting. Consequently, it may be assumed
that the respective gene si4 is absent from the
Newfoundland/Landseer breed. In the dark Newfoundlands, the minor spotting
genes s2and s3, established for the Landseers, may be
present. In order to investigate the effects and the inheritance of these
minor spotting genes independent from a major spotting gene, the white
marks of Newfoundlands are of interest. Therefore Mrs. Karin Brönnecke, a
breeder of black and piebald Newfoundlands, evaluated the Swiss Dog Stud Book (SHSB)
up to 1979 for matings between phenotypic grades of dark Newfoundlands.
Primarily she distinguished between cases of different distributions of
white marks. After putting together related patterns, the following main
classes were established:
| class I | self-coloured without any white marks | |
| class II | small white marks are present, restricted to the breast and paws | |
| class III | 'pseudo-Irish' type of spotting: marks which are found at the same places of the body as in class II, are enlarged remarkably or additional marks appear, especially at the head, belly and the tail tip. |
The most common phenotype of class II has only a white breast spot. A very small number of animals bear marks restricted to one or more paws. Both types are included in subclass IIa. The rest, forming subclass IIb, are marked on the breast as well as on one or more paws. Thus the phenotype of IIb represents a stronger spotting type than IIa from a qualitative point of view.
Hypothetical genotypes related to classes of self-coloured and white marked phenotypes
With respect to the piebald spotting locus S, the S1+S1+ and S1+ sp1 genotypes are possible within the self coloured Newfoundlands. As piebald offspring are very rare within this breed, the gene frequency of sp1seems to be extremely low. Therefore the piebald spotting gene shall be neglected in the following. We assume that a single sp1gene has no influence on the intensity of white marking, but strictly this may not be true. In any case, completely self-coloured offspring have been reported from Newfoundland x Landseer crosses. Thus we propose to analyse the phenotypic effects of the minor spotting genes s2and s3 on the base of a 'self-coloured' background with respect to major spotting genes.
The main assumption is that s2and s3 act as incomplete recessives. No marking effect will be generated by the heterozygous genotypes S2s2S3S3 , S2S2S3s3 and S2s 2S3s3. Thus s3, which acts as a dominant in combination with sp1sp1 , should have a small letter, even in the previous section (p. 000).
Class II contains all genotypes with one homozygous minor spotting gene. In this condition, a weak effect is proposed if additionally a single copy of the other minor spotting gene is present. Then, a stronger expression of marking should appear. The effect is so small, that it is not always visible. This can be concluded from the observation that one leg, left or right, may be spotted, while its opposite is not marked. Thus, the left and right leg may both be self-coloured, although genotypically marks could appear. It was not possible to establish two genotypic subclasses IIa and IIb, but one can assume that the genotypes containing three spotting genes are enriched in phenotypic subclass IIb and reduced in phenotypic subclass IIa.
The double homozygous s2s2s3s3 will be put in a class of its own as a remarkable increase of white spotting has to be expected from the general property of spotting genes of mutual enhancement. The result could be a pseudo-Irish type of spotting.
This is the complete list, relating genotype to phenotypic class:
| Genotypes | Phenotypes | ||
Sp1 | S2+S2+ | S3+S3+ | class I |
| Sp1 | S2+s2 | S3+S3+ | |
| Sp1 | S2+S2+ | S3+s3 | |
| Sp1 | S2+s2 | S3+s3 | |
Sp1 | s2s2 | S3+S3+ | class II |
| Sp1 | S2+S2+ | s3s3 | |
| Sp1 | s2s2 | S3+s3 | |
| Sp1 | S2+s2 | s3s3 | |
Sp1 | s2s2 | s3s3 | class II |
Results of crosses amongphenotypic classes of dark Newfoundlands
Table 6. Results of crosses among Newfoundlands of various spotting classes regarding white marks.
| Matings between spotting classes | Spotting classes of offspring | Observed values | Expected values for S2, S3 | Gene frequencies S2, S3 | χ2 | Probability P | ||
|---|---|---|---|---|---|---|---|---|
| I x I | I | 1765 | 1740 | 0.65; 0.65 | 2.62 | 0.11 | ||
| II | 234 | } 234 | 250 | } 259 | ||||
| III | 0 | 9 | ||||||
| I x II | I | 627 | 641 | 0.65; 0.65 | 0.94 | 0.34 | ||
| II | 320 | } 323 | 293 | } 309 | ||||
| III | 3 | 16 | ||||||
| IIa x IIb | I | 12 | 15.4 | 0.65; 0.65 | 1.13 | 0.58 | ||
| II | 37 | 36.9 | ||||||
| III | 5 | 3.8 | ||||||
| II x II | I | 88 | 88.3 | 0.65; 0.65 probability of genotypes s2s2S3+s3, S2+s2s3s3 devided by 4 | 4.96 | 0.09 | ||
| II | 127 | 130.2 | ||||||
| III | 6 | 2.5 | ||||||
The evaluated breeding data were collected to give a set of matings (Table 6). The procedure to test the hypothesis is the same as for the piebald spotting studies. As some phenotypic classes contain more than one genotype, the variation of offspring depends on the gene frequencies. The hypothesis presented in the above sector gives a good agreement with the observations in a wide range of gene frequencies, in contrast to the author's calculations for other modes of classing genotypes to phenotypes.
In the matings I x I and I x II, the offspring classes II and III have been put together for statistical calculations, as the reported values of class III are surely lower than the true values. This has to be expected from the practice of breeders to reduce the number of puppies in a litter and to eliminate the disliked, heavily white marked class first of all. Especially in matings between class-II parents, the special condition of dog breeding in contrast to scientific breeding experiments has to be taken in account. Whereas in the mating I x II the white marking of the class-II parent will be compensated by the other parent and all individuals of class II can be used, in the mating II x II, which is very risky, only individuals with very faint white marks will be mated. This selection within class II can be simulated by reducing the probability of the genotypes s2s2 S3+s3 and S2 +s2s3s3 to one-fourth of the equilibrium value in the population for the mating II x II. On the other hand, the conditions comparable with a planned breeding experiment are maintained, if all matings are collected where one parent is faintly marked and the other has a more heavy expression of white marks, which means IIax IIb matings.
The statistical tests yield high probability values P for individual matings as well as for the complete set, calculated for the gene frequencies regarded as representing the equilibrium state during the considered breeding period. The best fitting gene frequencies are 0,35 s2 and 0,35 s3. Compared with the Landseer breed, the gene frequencies of the minor spotting genes have been slightly reduced.
Furthermore, the inheritance of the white breast spot is better explained by a hypothesis involving two recessive spotting genes than by a single dominant as proposed by Wegner (1979).
Conclusions
In dog
and cattle breeds selected for piebald spotting with the 'large spots'
pattern as the most desired type, inheritance of spotting can be explained
by a recessive major spotting gene sp1, working
with at least two modifying genes s2 and s3
, one of them, s2, being regarded as a recessive, the other,
s3, as a dominant on the sp1
sp1background. From this
interaction of genes results phenotypic variation reaching from the
relatively dark 'Mantel' type to the almost white 'restricted spots' type.
The modifiers act as minor spotting genes in their own right on an
S1+ background. As s3 is a recessive without mutual
enhancement with other homozygous spotting genes, it is written in small
letters. The variation of phenotypes reaches from pure self-coloured to
'pseudo-Irish' marked.
Whereas
in piebald phenotypes, the head region is least affected by the restriction
of coloured area, quite the opposite is true in the original 'lrish' type
of dog spotting. Therefore a major spotting gene si4
non-allelic to sp1 has been assumed.
Homology between sp1of dogs and h of the Norway
rat, postulated by Little (1957, 1958), has to be rejected, because the
patterns are quite different. lf independent, the major spotting genes
si4and sp1can be combined in a double
homozygous individual, which will be restricted in the anterior part as well as
in the posterior part of the body with respect to plate development. The result will be 'almost white'
in phenotype. In breeds which are homozygous for si
4, a bimodal distribution of phenotypes
has to be expected with a maximum for the 'lrish' type and another for the 'almost white',
separated by a gap. Exactly this happens in Boston Terriers, Bull Terriers and Boxers (Little,
1958).
The
factor sw of Little's hypothesis (1957, 1958) proved to be unnecessary, as
the respective phenotype can be explained by homozygous sp1,
enhanced either by two minor spotting genes
(s2s2S3s3s2s2s2s3)
or by the Irish spotting gene (si4si4).
These
studies were performed to find out what happens if self-coloured and
spotted strains of related breeds are cross-bred. Will there, for instance,
be an increase of white marked Newfoundlands or of dark Landseers? This is
a question of the minor modifiers s2and s/3
and not of the piebald spotting gene. As both
breeds, each selected for desired types, differ in modifier gene
frequencies, an uncontrolled mixture would give unfavourable results. On
the other hand, with aid of 'Mantel' type Landseers, the gene frequency of
at least s3 could be reduced in Newfoundlands.
lf interested in Iarge spots' type Landseers out of S1+
sp1
Newfoundlands, one should avoid
mating unmarked Newfoundland x 'Mantel' type Landseer and heavily white
marked Newfoundland x 'restricted spots' type Landseer.
Zusammenfassung
Die Vererbung der
Plattenscheckung und ihrer Variation bei schwarzbuntem Niederungsvieh und
Landseer-Neufundländer Hunden
Für Hunde- und Rinderrassen, die nach einem typischen
Plattenscheckungsmuster selektiert sind, läßt sich die Vererbung der
Scheckung mit Hilfe eines rezessiven Hauptscheckungsfaktors sp
1erklären, der unterstützt wird durch
wenigstens zwei Modifikatoren s2 und s3.
Einer davon, s2, wird als rezessiv
angenommen. Der andere, s3, soll dominant
sein, allerdings nur bei genetischem Hintergrund mit sp1
sp1. Aus dem Zusammenwirken dieser Gene ergibt
sich eine phänotypische Variation im Bereich von 'Mantelscheckung' bis zum
fast weißen 'reduzierten Plattentyp'.
Die Modifikatoren
wirken auf S1+ Hintergrund als selbständige schwache
Scheckungsfaktoren. Wenn kein anderer homozygoter Scheckungsfaktor zur
gegenseitigen Verstärkung da ist, ist auch s3 rezessiv und wird deshalb
mit kleinem Buchstaben geschrieben. Die Variation der Phänotypen reicht von
voll ausgefärbt bis zu 'pseudoirischer' Scheckung.
Während bei typischer Plattenscheckung die Kopfregion am wenigsten von
der Einschränkung der Ausfärbung betroffen ist, gilt das Gegenteil für die
echte 'irische' Scheckung beim Hund. Deshalb wird der Faktor si4
als nicht zu s1 alleler Hauptscheckungsfaktor für irische Scheckung angenommen. Der
Homologisierungsversuch Littles (1957, 1958) mit dem Locus h der
Haubenratte kann nicht nachvollzogen werden, da dieses Muster grundsätzliche
Unterschiede zur Plattenscheckung des Hundes aufweist. Wenn si
4und sp1unabhängig mendeln, können
sie doppelt homozygot zusammentreffen. Als physiologische Wirkung ist die
Einschränkung der Ausfärbung sowohl im vorderen als auch im hinteren Körperbereich
zu erwarten, so daß ein fast weißer Phänotyp resultiert. Dieser Typ sollte
bei Rassen, die homozygot in si4
sind und außerdem sp1enthalten, auftreten
und ein zweites Maximum in der Verteilungskurve der Phänotypen bilden. Das
ist tatsächlich bei den Rassen Boston Terrier, Bull Terrier und Boxer der
Fall (Little, 1958).
Littles Faktor swerweist sich als überflüssig, da der betreffende Phänotyp
bereits durch homozygotes sp1 erzeugt wird, wenn die
beiden Modifikatoren in den Kombinationen (s2s2
S3s3) und (s2s2
s3s3) oder homozygotes si4
vorhanden sind.
Diese Untersuchungen
wurden durchgeführt, um die Auswirkungen der Verpaarung eines ausgefärbten
und eines plattengescheckten Farbenschlages einer Großrasse zu verstehen.
Treten eventuell gehäuft unerwünschte Zeichnungen auf wie weiße Abzeichen
beim ausgefärbten Teil und zu dunkle Scheckung beim gescheckten Teil der
Nachzucht? Dies ist allein eine Frage der Modifikatoren s2
und s3. Die beiden verwandten
Rassen Neufundländer und Landseer unterscheiden sich in den Genfrequenzen
in der berechneten Weise. Eine unkontrollierte Vermischung würde tatsächlich
unerwünschte Ergebnisse bringen. Andererseits kann durch Einkreuzung von Landseern des 'Manteltyps' wenigstens
die Genfrequenz von s3in Neufundländern erniedrigt werden. Wenn das
Hauptinteresse an typisch plattengescheckten
Landseern mittleren Grades besteht, sind die
Paarungen Neufundländer ohne Abzeichen x Landseer mit Mantelscheckung und stark
gezeichneter Neufundländer x sehr heller
Landseer zu vermeiden.
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