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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.