The exploration of
the genetic basis of pigeon colors
Learning by doing works
sometimes. For complex questions about color inheritance in
pigeons rather not. It usually ends in the conviction that the
general inheritance laws do not apply to pigeons. Scientists
also took several decades after 1900 to obtain a satisfactory
classification of color classes. Before 1900, the color
gradations from black to white with their transitions were
described in great detail, e.g. in the book from Prütz of 1885.
Black was demarcated from blue. Blue was split into nuances such
as lighter and darker blue, silver and more lightening. Among
them, today surprising, also ash red red and ash yellow. Red,
yellow and brown colors, including bronze varieties, formed
another group.
The process of
enlightening of the genetic composition of the basic colors
Leon J. Cole (1877-1948)
was the first professor of genetics at the University of
Wisconsin. He showed in 1914 that there were two types of red,
one dominant red and one recessive. That sounds trivial, but it
was groundbreaking. Before, you could not tell the two types
apart. So there were unexplained contradictions in hereditary
experiments. It was discovered in the research group of Cole
that blue and black have the same basic color. It was also
recognized that Dominant Red was something else. Jan Metzelaar,
a Dutchman who worked at the University of Michigan, reported in
1924 on brown as an independent base color. It was only around
1930 that the epistatic character of Recessive Red over the
three primary colors was confirmed. In Fig. 1 they are therefore
found under all three primary colors. Besides the scientists
mentioned many others were involved in research, from different
institutions worldwide. In parallel, bronze, the dilution,
feather structures and others were investigated.
Fig. 1: Time Chart of
the Exploring the Relationship between the main Colorations
(Source: Sell, Genetik der Taubenfärbung (German language),
Achim 2015).
Exercises
The development of the
classification of the basic colors took about three decades.
Building on the state of knowledge, with suitable teaching
material it requires a day to understand the classification
according to genetic criteria. It takes a pencil and some paper
to use the Punnett square as a didactic aid to understand the
results of color crossings and use them for breeding planning.
However, it is useful to start on the first page of teaching
materials, not in the middle.
It is then easy to
explain why, in addition to black young cocks, a yellow male and
a black female suddenly have dun female juveniles in their nest
and that Mendel's 'Uniformity Law' has been repealed. Fig. 2 is
in a photomontage of Ancients (the blacks from 'Gieseke World'
and shown at the 3rd German Tumbler Show). But the results shown
can be reconstructed at any time with other breeds in one's own
loft.
From a genetic point of
view, it was not, as beginners suspect, only a yellow cock
paired with a black hen. The basic color of most of the
Recessive Reds and their dilutes, the Recessive Yellows are
black and most have the color spreading factor S as the blacks.
From a genetic point of view, from the base color black was
paired with black, which results in a black base color in
offspring.
From a genetic
perspective, on a second level, Recessive Red was paired with
Non-Recessive Red. From the investigations of Cole et al. we
know that the recessive red and thus the yellow are epistatic to
the basic color. With homozygosity present, it has covered the
black ground color in the yellow cock. Paired with blacks, which
we assume is not accidentally mixed with recessive reds, only
heterozygous recessive reds will come out of it. They, since
recessive, will not show the red color.
Yellow is a dilute color.
The dilution factor is inherited sex-linked recessive, as
already noted in 1913 by the Englishman Staples-Browne. This
brings into play the sex-linked inheritance that Mendel did not
experience. From a diluted-colored male all young females will
inherit the dilution factor and appear dun at black primary
color. Their brothers are only heterozygous for the dilution
factor, and as this is recessive, they will not show it. With
black basic color they are also phenotypical black.
Exercises with
Punnett’s Square
At the first level of
observation, the genetical base color, both the yellow and black
have a black base color. The two genetic information of the cock
are entered before the first column of the square, the genetic
information of the hen in the header. The four cells of the
inner square contain all theoretically possible combinations.
The base color is like the dilution sex-linked. Therefore, the
Punnett’s square with a 'dot' is chosen for the 'hemizygous'
females. They only have sex-linked one gene for color. Instead
of the symbols here the cursive is used. The youngsters are all
black from the primary color. Trivial, for beginners however is
the idea that an intense red or yellow hen could genetically
have a black base color, already hard to understand.
Fig. 3: Punnett Square
for Color
The second level of
consideration is the recessive red, which is to be considered in
the Punnett square for non-sex-linked genetic factors.
Fig. 4: Punnett's Square
for the Recessive Red
All juveniles are only
heterozygous recessive red, so that the factor cannot affect.
At the third level of
consideration we return to the Square of sex-linked genes. From
this point of view, a dilute-colored male is mated with a
non-diluted female. The female can only have one hereditary
information, which in the black female is the wild type,
non-diluted. The cock has twice the recessive dilution factor:
Fig. 5: Punnett square
for dilution
In female youngsters,
only the genetic information dilution appears, so they are also
diluted in appearance. In contrast, the cocks are only
heterozygous for dilution, but they will not show up since it is
a recessive factor.
Combination of
viewing levels
The young females have a
black base color, they have the recessive red only heterozygous
and are diluted. Thus, they are of the phenotype dun colored.
The young cocks have
also a black basic color, also the recessive red in
heterozygosity. Unlike the females, they are only heterozygous
for dilution. This makes them phenotypically black.
If you want to test your
understanding, you can try to figure out the result that would
have been expected if the black Ancient hen had been mixed for
recessive red. If you also want to train your dexterity on
Punnett's square, you can use the square to try to figure out
what it means for the inheritance of crest and to find out the
hen's genes with regard to crest, if some of the offspring like
in the montage show a crest.
Literature:
Axel und Jana Sell, Vererbung bei Tauben,
Reutlingen 2004
Axel Sell, Pigeon
Genetics, Achim 2012
Axel Sell, Genetik der Taubenfärbungen,
Achim 2015
www.taubensell.de
