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Wonder bags and their
genetic decoding
The importance of case
studies for the understanding of hereditary processes
The black pigeon and his
platinum-check hen are a 'wonder bag' in breeding. Five colourings
in nine kittens! Coincidence or genetically explainable? It is a
coincidence that just these colourings fell in the respective
numbers. The fact that they had to occur with a certain probability
due to the genetic disposition of the parents can be explained by
hereditary laws. One can even deduce probabilities for the next
breeding season.
Who cares about that? Some
will say, I don't know the breed. The colourings also seem strange
to me. Whoever thinks like that should not read genetic texts. He
can only be disappointed. For there is no special genetics for a
breed, only an application of genetics to breeds and traits.
Educators speak of exemplary significance in learning content. In
primary school, the multiplication task 15 times 13 is not set so
that children remember the result for the rest of their lives. The
methodology of written multiplication and mental arithmetic is
understood and practised: methodological competence, not the
memorisation of results!
It is similar here. Using
the example of the breeding pair, those interested can activate
their knowledge of Punnett's squares. They can reconstruct the
hereditary processes for the relevant hereditary factors. The
'genetics staircase' composed of the respective squares provides a
framework for systematically 'working through' the individual steps.
In summary, it leads to the answer to the question which colourings
can be expected from a mating and with which probability. In the
planning stage it provides the framework for systematic breeding
planning. Be it to avoid too close inbreeding by occasional crosses
when breeding with several colourings, be it to transfer breeding
progress from other colourings or breeds.
Fig. 1: Platin check hen and
black cock
Genetics of the parents:
The sire is heterozygous for the colour spread factor S. He is at
least heterozygous, but probably homozygous for the bar pattern
covered by Spread. Finally, he is heterozygous for the recessive
hereditary factor platinum. The dam is homozygous platinum, mixed
hereditary check/bar. She does not have the spread factor. Although
late mated, until now (August 2022) nine youngsters in five
colourings: three blue-bar, three Spread platinum, one blue-check,
one platinum-check and one platinum bar.
Didactics:
The methodical procedure in explaining the diversity of the
offspring can be illustrated by the image of the 'genetic staircase'
formed by Punnett's squares. Individual 'building blocks' of the
respective step are examined with known hereditary laws. The partial
results are combined, taking into account overlapping (epistatic)
effects and, if necessary, genetic linkages. Finally, the
summarising result is read off.
Fig.2: Genetics staircase
adapted to the problem
On the genetics of the
offspring on the individual steps:
Let's start 'going through' the 'stairs' at the top step. From the
mating 50% offspring with the dominant colour spread factor Spread
are to be expected (S//+), which they inherited from the sire who is
also heterozygous for Spread.
At the intermediate level in
the analysis of the inheritance of platinum, 50% should be
homozygous for the recessive factor platinum (pl//pl) in a large
number. Here it is 5 out of 9.
Finally, at the lower stage
in the patterns, 50% are expected to be barred (+//+) and 50%
checkered (C//+). Because of the epistatic (overlapping) effect of
spread over the patterns, the pattern is clearly only visible in
juveniles without spread. In the presented mating there are 4 barred
and 2 checkered. However, the experienced breeder will have a
reasonable suspicion in one of the three kittens with the spread
factor that the colour spread factor hides the bar pattern.
Not all possible colourings
have fallen out of the magic bag yet. Solid black is still missing.
The probability for black was ¼. Instead of the expected 1/8 blue
bars, 1/3 have fallen.
The genetic make-up of the
bred kittens:
·
The three blue kittens are mixed
platinum (+//pl) with the bar pattern and without spread.
·
The three solid coloured platinums
are homozygous platinum (pl//pl) and heterozygous spread (+//S).
·
The blue check one is mixed
platinum (+//pl), mixed checkered (C//+) and without spread (+//+).
·
The platinum check female is
purebred platinum (pl//pl), mixedbred checkered (C//+) and without
spread.
·
Finally, the barred platinum male
is pure platinum (pl//pl), also without spread (+//+).
Exemplary meaning:
The illustration can be transferred 1:1, e.g., to the mating of
silver (spread milky) Lahore with barred and checkered milky as well
as with the initial colour strokes. The word platinum is only to be
replaced by milky. One can easily make a modification to the
dominant factor indigo to include Andalusians. It is also easy to
integrate sex-linked factors such as Stipper, Reduced and Rubella by
adjusting the squares. Above all, one should realise how easy it is
for initially astonishing breeding results to explain themselves
with a structured approach. The real benefit of the systematic
analysis, however, does not lie in an explanation of the past, but
in the implementation of the gained competence for breeding
planning.
 
Fig. 3: Blue bar youngsters
 
Fig. 4: Spread Platinum hens
 
Fig. 6: Blue check, Platin
check and Platin bar
Concluding remarks:
The didactic concept related
to the current breeding activities in the author's loft has proved
helpful many times. It was already used as a leading idea on the
cover of the first brochure on pigeon genetics as a staircase-shaped
sequence of Punnett squares preceding the text. It can currently
also be found on the covers of the introductions to pigeon genetics
published in French, Dutch and English. A chance to familiarise
yourself with the implementation of inheritance rules in practice in
a playful way with examples and exercises given as supplement.
 
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