Blue is not
blue: smoky blue, dirty blue and variants in the domestic pigeons
A study by the University of
Texas (Krishnan / Cryberg 2020) sheds new light on the genetics of
the variants of the blue pigeon coloring. In pigeon breeds, the
color range extends from a delicate ice blue for ice pigeons and
damascene pigeons, a light blue for Hamburg tumbler breeds, and the
light gray pigeon blue adopted from the rock pigeon, to a dark
'strong blue' for Vienna Tumblers and related high-flyer breeds.
To the history:
In the variants deviating
into the dark, there are those with light beaks that lack the
otherwise existing white edged outer fane in the tail. They are also
available with dark beaks, mostly in the standard with dark blue to
black eye cere and with dark legs in the first weeks. The Dutchman
Bol had already investigated the second variant in 1926 when
analyzing the racing homer colors and determined the dominant
inheritance. 'Vetkleur' (strong color), adopted in English as
dirty, with the genetic symbol V.
Fig. 1: Dirty (Vetkleur) and the wild-type at
Racing Homer. Source: Bol 1926
The variant with a light
beak was analysed by W.F. Hollander in the 1930s with the result of
a recessive inheritance in mating with the wild type (Hollander
1938). As a symbol, sy was designated for smoky.
Variants of the blue
color in the sub-groups:
In breeding, the varieties
in fancy pigeon breeding have little contact. In some breeds the
color of the wild type with a dark beak was desired, in others the
light beak, and in others very dark blue pigeons with very dark
beaks. In the case of homing pigeons, in which all three variants
occur, the coloring is irrelevant anyway. However, there were
discussions about the correct color in some special clubs due to the
large range of colors shown in Fig. 2 and 3, both in the class of
dirty as in the class of those of smoky blue. Due to the color
differences within the groups, it was early assumed that there were
alternative genes (alleles) for variants of smoky as well as more
alternative genes of dirty with a similar but not identical
phenotype. This proposition can also be found in the most recent
study of this question from the University of Texas for dirty,
although the molecular genetic location of the V variants are not
lined out in the paper.
Fig. 2: Dirty Blue: Vienna Highflyer blue bar
(Jens Passeker) and Budaer Blue (Fred Wohlgemuth). Source: Sell,
Pigeon Genetics. Applied Genetics in the Domestic Pigeon, Achim
Fig. 3: Smoky-Blue at Memel Highflyer (Werner Rahlfs) and East
Prussia Tumbler (Hans Falk). Source: Sell, Genetik der
Taubenfärbungen, Achim 2015 (German language).
Fig. 4: Smoky Blue Racing Homer with a rather dark beak as adult
found in many smoky Racing Homers as well as the clouding in the
shield. At the right a rather dark smoky Stargard Shaker (Kai
Schnellbächer). Source: Genetik der Taubenfärbungen, Achim 2015.
Conjectures about Dirty and Smoky's genetic connections:
studies on the genetic connections of dirty and smoky and possible
alleles are missing. Some genetic interested fanciers were satisfied
with the indication that there could be alternative expressions of
the genes in question in both groups with slightly different
effects, so that there would exist alleles. Differences can also
result from the action of other (modifying) genes. Dirty and Smoky
for themselves can be seen as modifiers of the blue color and can
experience additional color changes due to additional factors acting
as modifiers. From this point of view, dirty could also be seen as
an additional modifying factor for smoky blues or - the other way
round - smoky as a modifier for dirty blue. This last hypothesis of
side-by-side independent factors has now been refuted by researchers
from Texas (Krishnan, Cryberg 2020) at least for the Smoky and Dirty
variants they tested. Thankfully, pigeons from the strain used for
testing are also shown so that you can see which variants have been
Fig. 5: Dirty, Smoky and the wild-type in der
Investigation of the University Texas (from left to right). Source:
Shreyas Krishnan, Richard L. Cryberg 2020
For the test:
The authors evaluated DNA
data from existing pigeon families, in which peculiarities were
found in some individuals due to deletions in areas which, according
to the findings, were also responsible for coding the coloration in
other species. The phenotypic examination identified these as smoky
when examining two close bred families. The recessive inheritance
known for Smoky from ‘classical genetics’ that follows the Mendelian
rules could be followed with DNA analyzes. The individuals in the
families were all phenotypically either dirty or smoky.
The following test was
carried out in the traditional way first to get some answers at
Available for tests were
smoky blues, from which it was assumed from the family tree that
they were also dirty. Coupled with a partner with the wild type, all
young should be at independent inheritance of dirty and smoky due to
the dominance of V dirty, unless the partner happens to be
At the first crossing, at
independent hereditary factors, all young would be heterozygous
dirty and thus dirty-colored because of the dominance of V. They
would also be split for Smoky, which would have no effect due to the
recessiveness. However, if the selected partner happens to be
heterozygous for Smoky, which cannot be seen because of the
recessiveness, then 50% of the young according to Mendel would be
homozygous Smoky and the other 50% heterozygous. Based on the
experience gained in the test, the young homozygous smoky under the
hypothesis of independent factors should cover V epistatically. In
that case 50% dirty and 50% smoky would be expected, none
individuals with the wild-type.
The result was something
completely different. Coincidentally, the partner was actually mixed
for Smoky. 3 of 9 young were smoky-blue. The remaining 6, however,
were not dirty, which they should have been according to the
epistatic model, they corresponded to the wild type. The conclusion
drawn from the result that the epistatic model should be rejected
and hypothesis 2 tested.
A model that is compatible
with the results of the pairing is the idea that Smoky and Dirty are
located at the same location at the relevant chromosome and are
therefore alleles in genetic terms. Pigeons can then be pure Smoky (sy
// sy), pure Dirty (V // V), mixed for each of the factors (sy //
V). In addition, of course, also mixed with regard to the wild type
(sy // + and V // +) and also wild type (+ // +).
The homozygous Smoky pigeons
chosen for the test was genetically characterized by sy // sy. A
partner from an unrelated strain that is mixed-smoky is sy // +.
Dirty (V) does not appear in either of the hereditary formulas and
therefore not in the offspring either. Only homozygous smoky (sy //
sy) and heterozygous smoky (sy // +) are to be expected. Hypotheses
obtained from empirical observations should be usually empirically
confirmed by independent series of tests, which can be easily made
up for by breeders in their own stock given the simple experimental
arrangement shown by the authors.
additional color factors:
The factors dirty and smoky,
in conjunction with other hereditary factors, also cause typical
changes that have been systematically compiled (Sell 2006) and are
shown below using the examples for dominant red. In combination with
the ice factor, dirty (for ice pigeons and damascene) and smoky (for
some Tumbler breeds) have typical effects that allow to identify the
traits also in these combinations.
Fig. 5: Dirty (at the left chart) and Smoky ash
red bar Pomeranian Eye Crested Highflyer compared to the wild-type
ash red bar at a Danzig Highflyer: Source: Genetik der
Taubenfärbungen 2015 and ‚Pigeon Genetics 2012.
for testing your own variants:
Tests can be carried out in
the traditional way by pairing pigeons with any colors that are
homozygous Dirty in one bird and homozygous Smoky in the other, and
both should come from a strain from long-term pure breeding, so that
no other recessive hereditary factors disturb the picture. Assuming
the validity of the hypothesis of the allelic relationship, a first
cross between Dirty and Smoky in the Punnett square can be
represented as follows:
All hatchlings are
phenotypically dirty, but heterozygous Smoky. When the young are
mated to one another, the picture becomes more varied.
Splitting the 1st generation
to generate the F2
There are dirty, homozygous
smoky and besides for dirty and smoky heterozygous individuals. From
the phenotype there are about a quarter smoky and three quarters
dirty. Three quarters, because due to the dominance of dirty, it is
not possible to differentiate between pure and mixed animals. We
will not raise any wild type individual.
We may compare the results
with the potential outcome at hypothesis 1. According to this model
of two factors acting in parallel, in addition to the majority of
dirty and a quarter smoky, 3/16 young individuals of the wild type
would also be expected. If an animal is raised that clearly
corresponds to the wild type (not smoky and not dirty), then the
tested variants are something else, the hypothesis would have failed
for these variants.
In principle, a breeder can
carry out the test with all color variants that he knows are
homozygous for Dirty or Sooty. Jokers should not, however, choose
recessive red, yellow or the diluted blue color or dilutes in
general, as these colors have a light beak even without smoky. Pieds
can also cause problems for the later classification of the young.
Fig. 6: Mating of a Dirty check Ice Pigeon cock
and an Ash Red hen with an ash red young cock and a black hen with
dirty beak and some black at the legs as indicator for Dirty.
The first part of a possible test was by
accident, and not related to the issue dealt with here, completed at
the same time as the report. For that purpose colors that are easier
to classify would have been used. A black check ice pigeon cock with
the dirty factor, paired with a Spread Ash Pomeranian with the smoky
factor, resulted in two young that were clearly phenotypically
identifiable as dirty. Gender-bound, and also easy to understand in
Punnetts squares, a Spread-Ash-colored cock with ink spots in tail and
primaries as a sign that he is heterozygous black, and a black hen
with a dark beak and slightly darkened legs.
In the F2 according to the allelic
model there should be no wild-type young among the now colorful
flock. There will be dominant red and black young in both sexes,
some black, some ashen, but also some blue check and ash red check,
and some of them will remember the grandfather's ice factor.
With their study, Shreyas Krishnan and Richard L.
Cryberg showed how molecular genetic studies and classic genetic
inheritance tests can be combined with benefits. The examined pigeon
families with the dirty and smoky factors were shown to behave like
alleles and not like independent hereditary factors when inherited
as was believed up to now. That would mean in consequence also an
adaption of symbols. The test procedure they have shown can easily
be traced in two generations by genetically interested breeders for
other strains and possibly other variants. Yet unanswered are the
causes behind the differences in the depths of color in both groups.
Genetic analysis of kleuren, veerpatronen, ink, en afteenkenigen bij
postduiven. Genetica 8: pp. 45-154.
Hollander, W.F., Inheritance of Certain
“Blue-Black’ Patterns and “Bleached” Colorations in the Domestic
Pigeon. Genetics 23 (1938), pp. 12-27.
Krishnan, Shreyas * and Richard L. Cryberg,
Department of Biology, University of Texas at Arlington, Arlington,
Texas, 76019, Effects of mutations in pigeon Mc1r implicate an
expanded plumage color patterning regulatory network, 2020, bioRxiv
preprint doi: https: / /doi.org/10.1101/792945. The copyright holder
for this preprint (which was not peer-reviewed) is the author /
funder. It is made available under a CC-BY-NC-ND 4.0 International
Sell, Axel and Jana Sell, Taubenfärbungen,
Colourations in the Domestic Pigeon, Les couleurs des pigeons,
Genetik der Taubenfärbungen, Achim 2012.
Sell, Axel, Pigeon Genetics. Applied Genetics in
the Domestic Pigeon, Achim 2012.