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Genetic linkages in pigeons - an often misunderstood inheritance mechanism

If two genetic factors both are located at the same chromosome, would they have to appear 'linked' again in later generations? That says the word linkage! Or not?

Every breeder can easily understand that the color genes lie on the sex chromosome. The male in pigeons has two chromosomes due to gender, the female only one. The daughters inherit their chromosome from the father, the sons one from the father and one from the mother. A blue pigeon (genetically black base color) with a dilute red pigeon (ash red or dominant red base color) produces heterozygous red cocks and blue hens.

The dilution factor is also on the sex chromosome. A dominant yellow cock (homozygous dilute) with a dominant red pigeon will produce heterozygous dilute red cocks and yellow females.

The third set of experiments affects both color and dilution. The mating of a pure-bred cock with a black base color and a yellow hen (dominant red + dilution factor) will result in red-colored cocks and black young females.

In the fourth test arrangement, this heterozygous red young cock is mated to a yellow hen. Due to the gender-specific inheritance, we know that all youngsters with a black base color are hens. You don't need a molecular genetic analysis or later observations of behavior. They are shown as a group in table 28 of the book ‘Taubenzucht’ and for the purpose of this contribution yellow marked.

Source: Taubenzucht, Achim 2019

Eight of the 17 black females were diluted. Black as the phenotype of the wild-type was thus separated from the wild type at the dilution locus in eight cases and associated with the dilution factor. The dilution and color gene on the chromosome are apparently so far apart that there is a break in the inheritance process and a new combination of the genes. Eight out of 17 make a crossing over and a new combination of 47% in black base colored females.

Source: Taubenzucht, Achim 2019. Outcome for the bilateral combination of color (black and ash red), beak length (long and short), breast frill (plain and frill) and dilution (dilute and non-dilute). Total number of backcross of F1-cocks to yellow Old German Owl hens 56.

To determine the overall crossover rate also for red and yellow hens and also for cocks, the sex of all youngsters would have to be determined by molecular genetic studies or behavioral analyses which is not included in this didactic demonstration. But even without this extension, the result of the study by Cole and Kelley (1919), almost 100 years ago, is confirmed. They found a relatively large distance and came to a crossover rate of around 40%.

In the last test arrangement not only the dilution and color expression are recorded, but also the length of the beak and frill or non-frill. As with many empirical studies, this study answers some questions, but also raises others.

Literature:

Cole, L.J., and F.J. Kelley, Studies on inheritance in pigeons. III. Descriptions and linkage relations of two sex-linked characters. Genetics 4, 1919, pp. 183-203.

Sell, A., Pigeon Genetics. Applied Genetics in the Domestic Pigeon, Achim 2012.

Sell, A., Taubenzucht. Möglichkeiten und Grenzen züchterischer Gestaltung, Achim 2019.