Molecular genetic investigation of the Stipper gene and its alleles
It has been a few years since Rebecca Bruders has called breeder in
North America to assist a molecular genetic study on almond-colored
pigeons with the supply of feathers and information. A preliminary
study has now been published, and a thank you went to Ken Davis and
Tim Kvidera. Almonds show a brown-yellow (almond-colored) plumage
with black flecks and, in the exhibition-classes, tail and primarier
as tricolor as possible with the colors brown/yellow, black and
white. Homozygous cocks are almost white and often show eye defects.
The essential gene is also present in the color-classes stippers and
sprinkles in different breeds.

Fig. 1: English Short Faced Almond Tumbler, Portuguese and Danish
Tumblers (Source: Sell, Pigeon Genetics, Achim 2012)
From the abstract of the authors: “By
comparing the genomes of Almond and non-Almond pigeons, we
discovered that Almond pigeons have extra copies of a chromosome
region that contains a gene that is critical for the formation of
pigment granules. We also found that different numbers of copies of
this region are associated with varying degrees of pigment
reduction. The Almond phenotype in pigeons bears a remarkable
resemblance to Merle coat color mutants in dogs, and our new results
from pigeons suggest that similar genetic mechanisms underlie these
traits in both species. Our work highlights the role of gene copy
number variation as a potential driver of rapid phenotypic
evolution.”
Copy number variation is a relatively new discovered form of
structural variation of the genome by duplication of the genes so
that they can be present in the region in multiple copies. Examined
and identified as alleles besides St were Qualmond, Sandy, Frosty,
Faded, Chalky, and White Out, a variant recently pointed out by Tim
Kvidera. Found and documented were the serious eye defects in
homozygous Almond cocks.

Fig. 2: St-linked Phenotypes (Source: R. Bruders et al. 2019)
In their Fig. 4 individuals examined, inclusive of considered
alleles of St, are documented. The Almond shown is not the
exhibition color class of almond English Short Faced, but it is a
more whitish stipper-like individual. Such birds also have the
stipper factor as a triggering element, so it is irrelevant to the
investigation. In the photo of the sandy pigeon also the color
spreading factor (S) could be involved in the coloring to get a more
stipper-like appearance. In Frosty Tim Kvidera has provided a photo
that shows the color as it is present also in homozygous Thuringian
gray-ground color cocks. Frosty females show no or barely noticeable
deviation from the wild type. For Faded, either a hemizygous hen or
a heterozygous Faded-cock is shown, which at a comparison with
Frosty could irritate those not familiar with these traits. In terms
of terminology, Almond sometimes appears as a coloration, then
alternative as a gene instead of the term Stipper with the symbol St
introduced by Christie and Wriedt. It remains recognizable, however,
what is meant in each case.
Hopefully the announcement of the authors to pursue the topic
further will become true since the study even now brought a lot of
important insight.
Literature:
Bruders, Rebecca, Hannah Van Hollebeke, E.J. Osborne, Zev Kronenberg,
Marc Yandell, D. Shapiro, A copy number variant is associated with a
spectrum of pigmentation patterns in the rock pigeon (Columba
livia),
doi: https://doi.org/10.1101/688671
https://www.biorxiv.org/content/10.1101/688671v1?fbclid=IwAR2LvknbI3GD0-duTMApYq-tbJPbPflm4F_QNxpdUdhXg44HtU4N5zg-u7Y
Sell, Axel, Pigeon Genetics. Applied Genetics in the Domestic
Pigeon, Achim 2012.
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