Genes and the combination of genes in domestic
pigeon colourings
Genes as carriers of hereditary information
Genes are a small section on a chromosome which
are characterised by a certain effect. In the case of the mutation
of the black basic colour to ash red, this effect lies in the change
in the mixing ratio of black and red pigments in favour of the red
pigments (phaeomelanin). At the same gene locus, the mutation to
brown occurred with a different mixing ratio. The mutation from the
bar pattern of the wild-type to checks at a different location in
the genome causes check spots in the wing shield. At the same gene
locus there were mutations to a darker check (T-check) and to the
omission of the bars (barless). Further mutations occurred elsewhere
in the genome, which in their combination contributed to the variety
of domestic pigeon colourations, which are impressively recorded in
colour photographs by Levi in the Encyclopedia of Pigeon Breeds
1965, and also by others in later books.
Combinatorics using the example of the basic
colours and the pattern genes
Three basic colours (black, ash-red and brown)
and four markings (barred, barless, check and T-check) result in 3 x
4 = 12 colourings of the domestic pigeon. In appearance, there are
barred, barless, checks and T-checks on blue, ash-red and brown
ground colour.

Fig. 1: The base colours black, ash red and
brown. Source: Sell, Pigeon Genetics 2012
Epistatic effects using the example of the colour
spread factor
If a third level is added, the factor 'spread' as
a mutation from wild type, then there are 3 x 4 x 2 = 24 genetically
different genotypes. However, apart from small differences due to
hetero- and homozygosity, there are only 15 phenotypes: (3 X 4) + 3
(cf. figure 5 in the appendix). This is because Spread largely
covers pattern. In genetics as 'epistatic' taken from the Greek.
With a black ground colour, one obtains blacks of varying intensity,
Spread Ash that vary more in colouration, and solid browns.

Fig. 2: Spread on a black, brown and ash red
colour base. Source: Sell, Pigeon Genetics 2012
Gaining knowledge in the early phase of Mendelian
hereditary analyses
When dominance, recessivity, epistasis and the
combinatorial effects were found through classical hereditary
experiments in the first half of the last century, it was known that
the Mendelian hereditary factors were located in the chromosomes
(Richard Goldschmidt, ‘Die Lehre von der Vererbung’, 2nd edition 6th
- 10th thousand, Leipzig 1929, p. 106). Here this source is quoted
with the edition number, which shows the interest in scientific
questions at that time. The exact location of the genes and the
concrete image of the DNA were not known. It was obvious to breeders
and interested scientists that the pattern of bars, barless, check
and T-check of the blue colour (black ground colour) were repeated
in the ash red and in the brown series. The genes were not
identified in the laboratory, but by their effects in appearance.
This is also how the check gene (C) got its name, flecks in the
shield as if hit with a hammer on cold sheet metal. That the pattern
did not only exist in the imagination of the scientists could and
can easily be shown by the fact that, e.g., the pattern for the
check is transferred from one basic colour to the other according to
Mendel's rules. This can also be easily shown for the colour spread
factor, when Spread Ash mated with blue bar or blue check produce
black kittens as well as Spread Ash. This is also true when the blue
check cock has additional modifying hereditary factors, such as ice
colours in the attached picture from an own recent cross.

Fig. 3: Transfer of the spread gene from a Spread
ash red hen to the black ground colour resulting in Spread ash red
cocks and and black hens. Source: Sell, Critical Issues in Pigeon
Breeding Part VI (2021)
When the illustration of the interaction of the
three factor groups like that from ‘Breeding and Inheritance in
Pigeons’ in Figure is presented, there will always be someone who
protests by saying that he has also raised 'blacks with even blacker
bars' from the mating of blue with black. These are weakly coloured
blacks with bar markings, distinguished from the darker blacks by
modifiers, and are found in many such matings. These aspects are
dealt with in the better textbooks after the basic introduction.
Such features are also the subject of the series 'Critical Issues in
Pigeon Breeding'.
Gaining knowledge in molecular genetic studies
With the development of molecular genetics, genes
gained a face in the form of detectable base sequences in certain
stretches of chromosomes. This also made it possible to look for
differences and similarities in the DNA of individuals with certain
characteristics in these sections. It is thus possible to show that,
for example, individuals with ash-red colouration systematically
have a different base sequence in a certain region than, for
example, pigeons with wild-type colouration. If in the experimental
analysis the identity of the colour spread factor in Spread Ash and
black has been shown by transferring the spread factor of Spread Ash
through crosses with blues or checks to blacks, this can be done
molecularly in the laboratory by comparing the relevant genomic
regions. Epistatic and combinatorial effects was then also the title
of an article in which the basic framework of the interaction of
hereditary factors obtained in classical genetics is underpinned by
molecular genetics (Domyan et al. 2014).
The importance of molecular genetic studies for
the practice of pigeon breeding
As stated in the study by Domyan et al (2014),
the relationships of dominance and recessivity to each other and the
hierarchical relationships of essential hereditary traits are known
through classical genetic studies. What has not been uncovered are
the molecular genetic peculiarities of these gene loci and the
mechanisms of their interaction, which the cited studies contributes
to deciphering. If one knows where in the genome certain hereditary
information is stored and the base sequence of the DNA sections
(genes), then it will also be easier to decide whether similar
phenomena are based on identical genes, alleles or other genes with
similar effects. It would be interesting for those interested in
genetics, especially in the case of the bronze and grizzle variants,
which differ externally and also in their heredity. In the case of
grizzle varieties, for example, fifteen varieties alone were
described in the 2012 book 'Pigeon Genetics'. Studies in recent
years have also shown that in pigeons not only the base sequence is
responsible for trait expression, but also, for example, copy number
variations can be present. Genes are then present in increased or
decreased copy number (Bruders et al. 2020, and briefly in Critical
Issues Part IV).
Heredity and pigeon breeding
For the practice of pigeon breeding, the
molecular genetic studies represent a confirmation of the results of
a century of classical genetic analyses. They thus indirectly
confirm the breeding strategies derived from classical genetics. Not
only for the factors presented above. Actually, one would expect
that this would also increase the interest of breeders in heredity
issues. Rather the opposite is the case. Of the members active in
the pigeon fancier forums on the internet, far more than half will
not remember the name Punnett. And of the others, only a minority
will know what the didactic tool of Punnett's squares in breeding
planning is all about. For breeders more deeply interested in
genetic questions and mechanisms, it is a stroke of luck that
molecular geneticists have been able to bring the domestic pigeon
back into academic research as an object of study. Others usually
already have problems in classical genetics with the symbols used
only as abbreviations for longer names of hereditary factors. For
them, the new terminology seems to build up rather greater fears of
contact, despite all the bridging aids (AS).
Literature:
Bruders, Rebecca u.a., A copy number variants is
associated with a sprectrum of pigmentation patterns in the rock
pigeon (Columba livia), PLOS Genetics, open access, Published May
20, 2020.
Domyan, Eric T., Michael W. Guernsey et al,
Epistatic and Combinatorial Effects of Pigmentary Gene Mutations in
the Domestic Pigeon. Current Biology 24, 459-464, February 17, 2014.
Goldschmidt, Richard, Die Lehre von der
Vererbung, 2nd edition 6th - 10th thousand, Leipzig 1929.
Levi, W. M., Encyclopedia of Pigeon Breeds,
Jersey City 1965.
Sell, Axel, Breeding and Inheritance in Pigeons,
Hengersberg 1994.
Sell, Axel, Critical Issues in Pigeon Breeding.
What we know and what we believe to know. Anecdotal, Entertaining,
and educational comments on open questions, Achim 2021.
Sell, Axel, Pigeon Genetics, Achim 2012.
Annex

Figure 4: Sell, Axel, Pigeon Genetics, Achim 2012
and Breeding and Inheritance in Pigeon 1994.
Fig. 5: Combinatorial and Epistatic Effect at the
example of base color, pattern and Spread. Source: Sell, Axel,
Breeding and Inheritance in Pigeon Breeding, Hengersberg 1994.

Fig. 6: Sell, Axel, Critical Issues in Pigeon
Breeding, http://www.taubensell.de
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