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Extreme sexual dimorphism in the domestic pigeon due to the
combination of hereditary factors: Frosty and Rubella
When surprising new colors
appear in a pigeon population, many think of mutations. Possible,
more likely, is an unknown interaction of hereditary factors present
in the stock. The combination of Frosty and Rubella is not a single
individual. It is a family that inherits the color sex dimorphism
with very light cocks and darker pigeons in the family. The
distinctive dimorphism gets lost through crossings with other colors
and improper further pairings. From Frosty's point of view, adding
rubella as a modifier reinforces the weaker gender dimorphisms
present in pure Frosty. From the Rubella's point of view, it is
noteworthy that a recessive factor like Frosty causes a color change
in both females and cocks. Beyond the case, an indicator that an
interaction of two recessive genes with intermediate phenotypes or
color changes in the F1 does not mean in all cases that
allelic relationships exist.
Fig. 1: Homozygous Frosty
Rubella cocks with the hidden soft bar pattern (left) and check
pattern (right)
Fig. 2: Pair of
Frosty-Rubella with a sex-related light male and a darker female
Fig. 3: Hemizygote
frosty-rubella females with check and bar pattern
Fig. 4: Hemizygous
dilute-colored frosty-rubella hen with check pattern
Frosty and Rubella:
Similarities and Differences
Frosty and Rubella are both
sex-linked recessive. Both factors are on the sex chromosome, but in
different places and not close together (Sell 2012, 2015). The known
color combinations for both factors are raised with a genetically
black base color. For both factors, inheritance is referred to as
sex-linked recessive. However, the inheritance patterns show an
essential difference. If you mate a bar rubella cock with a blue hen
without the factor, then the hens are rubella-colored and the cocks
are blue. If you mate a frosty cock on an otherwise blue basis (in
the standard blue-ground color) with a blue hen without the frosty
factor, then the hens are also blue. These young females have
hemizygous the frosty factor due to their sex (they are purely for
the factor in breeder jargon), but do not show it, like their
heterozygous brothers.
Frosty
A basic type of Frosty pair
appears as a blue-ground colored male with a blue bar female.
Frosty-colored variants are bred with check and bar pattern.
Thuringian Selfs as color breed are recognized in the standard as
not only non-diluted but also diluted frosty. These are the color
class 'yellow ground color' (diluted frosty check) and 'light ground
color' (diluted frosty bar) for cocks as well as the female color
classes larked (dilute frosty check) and silver (dilute frosty bar).
The here tested frosty are derived from that source. You can find
pigeons with the frosty factor abroad in homers with the same kind
of inheritance. However, the stocks were not tested against each
other.
Fig. 6: Frosty and diluted
Frosty in Thuringian Selfs. On the left a muffed pair with a
blue-ground frosty cock and a hemizygous blue frosty hen, in the
middle a hemizygous dilute-colored larked Frosty hen and on the
right a homozygous, diluted, ‘yellow-ground-colored 'cock. Source:
Sell, Taubenzucht (2019)
Some breeders believe that they
can recognize differences from the wild type in some blue Frosty
females and would like to speak of dominance. To speak of dominance
when more or less reliable indications for the factor are only found
on closer inspection and a DNA analysis is still needed to validate
it, then the term 'recessive' becomes worthless for breeders as a
rough orientation. What is striking about Frosty is the yellowish
coloration of the homozygous diluted cocks (Fig. 6), which can be
found in the diluted frosty-rubella hens (Fig. 4).
Rubella
Rubella is found in racing
homers and in lofts of breeders of rare colored homers, often with
the Spread factor. They are variable in color. This is in some lofts
partly due to pairings with the allele Reduced. It is often also
crossed with recessive and dominant opal, indigo and others. Even
without these ingredients there are deviations. The author has
experience with this (see Fig. 7 left). More bluish and more reddish
individuals, the latter often females and occasionally in the same
nest as a bluish young! Also dirty and smoky blue, with which a
clean blue and an almost white tail band result in attractive
variants that can be selected for. The color spread factor initially
led to sex-related lighter rubellas and darker females (Spread
Rubella). This distinguishing feature has disappeared over the
generations, and not just in our own stock.
  
Fig. 7: Pair of rubella
check and rubella bar with different hues, dilute bar rubella and
particularly pronounced white tail band in a smoky blue rubella cock
The dilution, introduced
into this family for test mating only by crosses with dilute-colored
Frosty, had a similar effect as with diluted blues in a lighter
shade.
Frosty-rubella
The creation process of the
combination was presented elsewhere. The combination of Frosty and
Rubella in the same pigeon finally resulted in the unexpected
appearances shown (Fig. 1-4). In the hen the rubella-colored bars
and checks became more delicate and came closer to Reduced. The
strong bleaching of the tail band of most rubellas was lost in the
hemizygous females by adding Frosty. The color appears overall more
ice-colored.
 
Fig. 8: Frosty Rubella hen
with the check pattern and a Frosty-Rubella young cock on the cover
of the book 'Taubenzucht' (2019)
From Frosty's point of view,
the colored sexual dimorphism is intensified with almost white cocks
and translucent reddish checks or delicate bars, as with the young
cock on the cover of 'Pigeon Breeding - Possibilities and Limits of
Breeding' in German language (Fig. 8). From Rubella's point of view,
adding the frosty factor in the bar and check variants creates a
color gender dimorphism. Interesting to remember that in
combinations with Spread we had it in the first years after the
discovery of Rubella in Spread Rubella. But it has now disappeared
there.
Documentation of
combinations with heterozygous and homozygous individuals
Hen:
At hens both factors can be
absent, they can have Frosty or Rubella, and they can have Rubella
and Frosty at the same time. There are four possibilities.
Fig. 9: The wild type
blue-bar in comparison with Frosty, Rubella and Frosty-Rubella
(picture right) in hens
Cocks:
Cocks can lack the rubella
factor, they can be heterozygous or homozygous. The frosty factor
can be lacking, can be present heterozygous or homozygous. This
results in 3 x 3 = 9 possibilities. The compilation shows the most
frequent and thus provisionally classified as typical phenomena as a
guide.
Fig. 10: Comparison of
phenotypes for pure and heterozygous individuals. Picture bar above:
Wild-type blue-bar, heterozygous rubella and homozygous rubella
(from left to right); picture bar in the middle: heterozygous
frosty, heterozygous frosty + heterozygous rubella, heterozygous
frosty + homozygous rubella (from left); picture bar below;
homozygous frosty (blue-ground colored), homozygous Frosty +
heterozygous rubella, homozygous Frosty + pure Rubella (from left)
Pairing options
Frosty Rubella can be paired
with each other in the strain and will always produce light-colored
cocks and darker females. The combination only proves to be fragile
in the case of pairings with other colors because Frosty and Rubella
lie together on the sex chromosome, but so far apart that the
connection in the inheritance after outside pairings often breaks
due to a crossover.
A Frosty Rubella hen will
breed heterozygous young for both factors with a cock lacking these
traits. When mated back to a Frosty Rubella hen, the youngsters of
the above pairing give you some Frosty- Rubella hens and a few
homozygous Frosty-Rubella cocks. Some Rubella hens and some Frosty
hens also occur due to a break of the linkage. The latter cannot be
differentiated with certainty from the wild-type hen. In the case of
the cocks, in addition to homozygous Frosty-Rubella, there will also
be a few heterozygous-breeds, such as the cock itself. By breaking
the linkage, some that are homozygous rubella and heterozygous
Frosty, as well as some homozygous Frosty, heterozygous rubella.
Anyone who has a small
Frosty Rubella family and is aiming for an external mating in order
to avoid the risk of breeding too close relatives can best do it
with a mating of a blue or blue check hen without risking the
preservation of the sexual dimorphism. And these from a stock in
which no other color factors are present. If only the frosty-rubella
hens from it are used for further breeding, the breeder does not run
any risk of maintaining the dimorphism.
Documentation of the
breeding year 2020
In 2020, four pairings were
carried out in our own loft in order to secure the experience gained
and to gain greater security when assessing heterozygous
individuals. The results are briefly commented on in order to give
breeders who want to experiment with these combinations an
orientation aid and, if necessary, to make their own deviating
assessments. In addition to the four cocks of the four pairings with
the participation of Frosty and Rubella, there were two homozygous
cocks and one black heterozygous Rubella cock in the stock.
Incorrect fertilization is therefore not excluded, but limited to
these cocks.
Mating 1
in Fig. 11 is the only mating from which homozygous
Frosty-Rubella cocks could have been raised. But they are not. The
prerequisite for this would have been that the hereditary factors
Frosty and Rubella on one chromosome of the father would have been
transferred together (linked) to a son. But sons can also inherit
the second chromosome and there can also be a break of the linkage
and a crossover. Three yellowish females can be classified as
hemizygote, dilute-colored Frosty-Rubella. They show that their
father is not only heterozygous frosty and rubella, but also for the
dilution factor. The first two bluish cocks are pure rubella
according to the phenotype and heterozygous for Frosty and thus the
result of a crossingover. The blue could be the wild type, but also
hemizygous Frosty without rubella cannot be clearly distinguished
from the wild type. This also applies to the two blue-checks
raised that
came after the grandmother in phenotype. Only one of these is shown
in Fig. 11.
Fig. 11: Three generations
in the picture. Grandparents a homozygous Frosty-Rubella cock and a
blue check hen with two of their young in the next line
(heterozygous frosty-rubella cock and a hemzygous frosty-rubella hen
and seven grandchildren.
Mating 2 in Fig. 12
consists of the true breeding Frosty Rubella cock shown in Fig. 1
with a Rubella hen with the Spread factor. One of her sons inherited
it, who is rated as pure rubella and heterozygous frosty (Fig. 12
left). In addition, a barred non-Spread brother. The blue cock in
the middle is also pure rubella, the light color of which may
indicate that the cock is heterozygous dilute.The next one is a
frosty-dilute hen. As the last young, a rubella bar hen was raised.
Rubella hens were to be expected. Due to the genes of the father,
but linked to Frosty. According to previous experience, such a
pigeon should not have had a clearly lightened tail like this hen.
The assumption goes back to a rubella cock as the biological father.
Fig. 12: Homozygous
Frosty-Rubella cock and a Spread Rubella hen with offspring
 
Fig. 12a: Close-ups of the
cocks of the first clutch from pairing 2: homozygous rubella +
heterozygous Frosty, right the same plus Spread
The 3rd pair in Fig. 13
consists of a Rubella male and a diluted Frosty Rubella female. The
cock comes from pure homing pigeons. The hen was raised from the
initial pairing shown in Fig. 1 as grandparents and is therefore a
sister of the female in pairing 1. Three females from pairing 3, two
of which are shown, could be classified as hemizygous rubella
without the Frosty factor. 2 checks and 1 barred cock met the
expectations for earlier homozygous rubella cocks with
heterozygosity for Frosty: The basic color is darker and the tail
feathers less lightened than with rubella pigeons lacking Frosty.
Fig. 13: Pure rubella cock
and a diluted Frosty Rubella hen with offspring
Surprisingly, three very
reddish youngsters, of which the first cock is shown in close-up in
Fig. 13a, with strikingly peppery wing and tail feathers. Possibly
heterozygous dilution might be of importance, but the other cocks
are also heterozygous dilute from the mother’s side. In the youngest
of the three reddish individuals, the bars also are bleached,
similar to homozygous Frosty cocks. Not clearly visible in the
photo, but like the Rubella sibling in the nest, still long-colored,
even if that was lost noticeably quickly after weaning.
 
Fig. 13a: Reddish cock of
the 1st clutch from pair 3, homozygous rubella, heterozygous frosty,
heterozygous dilution
The 4th pair in Fig. 14
consists of a wild-type blue homer, lacking other color genes as far
is known, and a Frosty-Rubella hen. Blue and blue check ones would
have been expected from this pairing without prior information, as
Frosty and Rubella are considered recessive factors. Nevertheless,
two young cocks who were heterozygous for the two factors from the
mother’s side showed color deviations in the check pattern (Fig.
14a) and confirmed earlier findings. The contrast to blue check may
be seen also in Fig. 14 by the blue check sisters. Another identical
non frosty-rubella hen from the pair is not shown in the picture.
Fig. 14: Blue-bar homer
(wild type) cock and Frosty Rubella hen with offspring
Fig. 14a: Wing shield of the
check youngsters with a brownish tinge of the checks (in Fig. 14 the
first and third young individual from the left)
Was nothing except
expenses?
Discussions about frosty and
rubella as rare factors will interest few pigeon fanciers. However,
some of the findings could be of general relevance. From the point
of view of inheritance mechanisms, the positive interaction of two
non-allelic recessive factors is remarkable (Fig. 10, 11, 14a).
Intermediate colorations and deviations from the wild type after
mating two recessive factors should therefore not be interpreted as
impartially as before as a sure sign of non-alleles. In the example,
the effects are particularly noticeable in the case of cocks that
are homozygous for both factors (Fig. 1). The example also shows
that with the introduction of a blue-bar hen supposedly
corresponding to the wild type, a hereditary factor may enter the
strain which only shows its full effects in the following
generations and can then trigger speculations about mutations. Many
reported mutations will instead be modifications. The study is also
an example of the fact that some questions could be solved, but also
new ones such as the explanation of the color deviations in pairing
3. Not yet mentioned but a possible research project could be the
observation previous to the parings discussed that the combination
of Frosty and dilution seemed to cause problems with vitality in
homozygous pigeons.
Literature:
Sell, Axel, Pigeon Genetics.
Applied Genetics in the Domestic Pigeon, Achim 2012
Sell, Axel, Taubenzucht. Möglichkeiten und Grenzen züchterischer
Gestaltung, Achim 2019 |
