Extreme sexual dimorphism in the domestic pigeon due to the combination of hereditary factors: Frosty and Rubella

When surprising new colors appear in a pigeon population, many think of mutations. Possible, more likely, is an unknown interaction of hereditary factors present in the stock. The combination of Frosty and Rubella is not a single individual. It is a family that inherits the color sex dimorphism with very light cocks and darker pigeons in the family. The distinctive dimorphism gets lost through crossings with other colors and improper further pairings. From Frosty's point of view, adding rubella as a modifier reinforces the weaker gender dimorphisms present in pure Frosty. From the Rubella's point of view, it is noteworthy that a recessive factor like Frosty causes a color change in both females and cocks. Beyond the case, an indicator that an interaction of two recessive genes with intermediate phenotypes or color changes in the F1 does not mean in all cases that allelic relationships exist.

Fig. 1: Homozygous Frosty Rubella cocks with the hidden soft bar pattern (left) and check pattern (right)

Fig. 2: Pair of Frosty-Rubella with a sex-related light male and a darker female

Fig. 3: Hemizygote frosty-rubella females with check and bar pattern

Fig. 4: Hemizygous dilute-colored frosty-rubella hen with check pattern

Frosty and Rubella: Similarities and Differences

Frosty and Rubella are both sex-linked recessive. Both factors are on the sex chromosome, but in different places and not close together (Sell 2012, 2015). The known color combinations for both factors are raised with a genetically black base color. For both factors, inheritance is referred to as sex-linked recessive. However, the inheritance patterns show an essential difference. If you mate a bar rubella cock with a blue hen without the factor, then the hens are rubella-colored and the cocks are blue. If you mate a frosty cock on an otherwise blue basis (in the standard blue-ground color) with a blue hen without the frosty factor, then the hens are also blue. These young females have hemizygous the frosty factor due to their sex (they are purely for the factor in breeder jargon), but do not show it, like their heterozygous brothers.


A basic type of Frosty pair appears as a blue-ground colored male with a blue bar female. Frosty-colored variants are bred with check and bar pattern. Thuringian Selfs as color breed are recognized in the standard as not only non-diluted but also diluted frosty. These are the color class 'yellow ground color' (diluted frosty check) and 'light ground color' (diluted frosty bar) for cocks as well as the female color classes larked (dilute frosty check) and silver (dilute frosty bar). The here tested frosty are derived from that source. You can find pigeons with the frosty factor abroad in homers with the same kind of inheritance. However, the stocks were not tested against each other.

Fig. 6: Frosty and diluted Frosty in Thuringian Selfs. On the left a muffed pair with a blue-ground frosty cock and a hemizygous blue frosty hen, in the middle a hemizygous dilute-colored larked Frosty hen and on the right a homozygous, diluted, ‘yellow-ground-colored 'cock. Source: Sell, Taubenzucht (2019)

Some breeders believe that they can recognize differences from the wild type in some blue Frosty females and would like to speak of dominance. To speak of dominance when more or less reliable indications for the factor are only found on closer inspection and a DNA analysis is still needed to validate it, then the term 'recessive' becomes worthless for breeders as a rough orientation. What is striking about Frosty is the yellowish coloration of the homozygous diluted cocks (Fig. 6), which can be found in the diluted frosty-rubella hens (Fig. 4).


Rubella is found in racing homers and in lofts of breeders of rare colored homers, often with the Spread factor. They are variable in color. This is in some lofts partly due to pairings with the allele Reduced. It is often also crossed with recessive and dominant opal, indigo and others. Even without these ingredients there are deviations. The author has experience with this (see Fig. 7 left). More bluish and more reddish individuals, the latter often females and occasionally in the same nest as a bluish young! Also dirty and smoky blue, with which a clean blue and an almost white tail band result in attractive variants that can be selected for. The color spread factor initially led to sex-related lighter rubellas and darker females (Spread Rubella). This distinguishing feature has disappeared over the generations, and not just in our own stock.


Fig. 7: Pair of rubella check and rubella bar with different hues, dilute bar rubella and particularly pronounced white tail band in a smoky blue rubella cock

The dilution, introduced into this family for test mating only by crosses with dilute-colored Frosty, had a similar effect as with diluted blues in a lighter shade.


The creation process of the combination was presented elsewhere. The combination of Frosty and Rubella in the same pigeon finally resulted in the unexpected appearances shown (Fig. 1-4). In the hen the rubella-colored bars and checks became more delicate and came closer to Reduced. The strong bleaching of the tail band of most rubellas was lost in the hemizygous females by adding Frosty. The color appears overall more ice-colored.


Fig. 8: Frosty Rubella hen with the check pattern and a Frosty-Rubella young cock on the cover of the book 'Taubenzucht' (2019)

From Frosty's point of view, the colored sexual dimorphism is intensified with almost white cocks and translucent reddish checks or delicate bars, as with the young cock on the cover of 'Pigeon Breeding - Possibilities and Limits of Breeding' in German language (Fig. 8). From Rubella's point of view, adding the frosty factor in the bar and check variants creates a color gender dimorphism. Interesting to remember that in combinations with Spread we had it in the first years after the discovery of Rubella in Spread Rubella. But it has now disappeared there.

Documentation of combinations with heterozygous and homozygous individuals


At hens both factors can be absent, they can have Frosty or Rubella, and they can have Rubella and Frosty at the same time. There are four possibilities.

Fig. 9: The wild type blue-bar in comparison with Frosty, Rubella and Frosty-Rubella (picture right) in hens


Cocks can lack the rubella factor, they can be heterozygous or homozygous. The frosty factor can be lacking, can be present heterozygous or homozygous. This results in 3 x 3 = 9 possibilities. The compilation shows the most frequent and thus provisionally classified as typical phenomena as a guide.

Fig. 10: Comparison of phenotypes for pure and heterozygous individuals. Picture bar above: Wild-type blue-bar, heterozygous rubella and homozygous rubella (from left to right); picture bar in the middle: heterozygous frosty, heterozygous frosty + heterozygous rubella, heterozygous frosty + homozygous rubella (from left); picture bar below; homozygous frosty (blue-ground colored), homozygous Frosty + heterozygous rubella, homozygous Frosty + pure Rubella (from left)

Pairing options

Frosty Rubella can be paired with each other in the strain and will always produce light-colored cocks and darker females. The combination only proves to be fragile in the case of pairings with other colors because Frosty and Rubella lie together on the sex chromosome, but so far apart that the connection in the inheritance after outside pairings often breaks due to a crossover.

A Frosty Rubella hen will breed heterozygous young for both factors with a cock lacking these traits. When mated back to a Frosty Rubella hen, the youngsters of the above pairing give you some Frosty- Rubella hens and a few homozygous Frosty-Rubella cocks. Some Rubella hens and some Frosty hens also occur due to a break of the linkage. The latter cannot be differentiated with certainty from the wild-type hen. In the case of the cocks, in addition to homozygous Frosty-Rubella, there will also be a few heterozygous-breeds, such as the cock itself. By breaking the linkage, some that are homozygous rubella and heterozygous Frosty, as well as some homozygous Frosty, heterozygous rubella.

Anyone who has a small Frosty Rubella family and is aiming for an external mating in order to avoid the risk of breeding too close relatives can best do it with a mating of a blue or blue check hen without risking the preservation of the sexual dimorphism. And these from a stock in which no other color factors are present. If only the frosty-rubella hens from it are used for further breeding, the breeder does not run any risk of maintaining the dimorphism.

Documentation of the breeding year 2020

In 2020, four pairings were carried out in our own loft in order to secure the experience gained and to gain greater security when assessing heterozygous individuals. The results are briefly commented on in order to give breeders who want to experiment with these combinations an orientation aid and, if necessary, to make their own deviating assessments. In addition to the four cocks of the four pairings with the participation of Frosty and Rubella, there were two homozygous cocks and one black heterozygous Rubella cock in the stock. Incorrect fertilization is therefore not excluded, but limited to these cocks.

Mating 1 in Fig. 11 is the only mating from which homozygous Frosty-Rubella cocks could have been raised. But they are not. The prerequisite for this would have been that the hereditary factors Frosty and Rubella on one chromosome of the father would have been transferred together (linked) to a son. But sons can also inherit the second chromosome and there can also be a break of the linkage and a crossover. Three yellowish females can be classified as hemizygote, dilute-colored Frosty-Rubella. They show that their father is not only heterozygous frosty and rubella, but also for the dilution factor. The first two bluish cocks are pure rubella according to the phenotype and heterozygous for Frosty and thus the result of a crossingover. The blue could be the wild type, but also hemizygous Frosty without rubella cannot be clearly distinguished from the wild type. This also applies to the two blue-checks  raised that came after the grandmother in phenotype. Only one of these is shown in Fig. 11.

Fig. 11: Three generations in the picture. Grandparents a homozygous Frosty-Rubella cock and a blue check hen with two of their young in the next line (heterozygous frosty-rubella cock and a hemzygous frosty-rubella hen and seven grandchildren.

Mating 2 in Fig. 12 consists of the true breeding Frosty Rubella cock shown in Fig. 1 with a Rubella hen with the Spread factor. One of her sons inherited it, who is rated as pure rubella and heterozygous frosty (Fig. 12 left). In addition, a barred non-Spread brother. The blue cock in the middle is also pure rubella, the light color of which may indicate that the cock is heterozygous dilute.The next one is a frosty-dilute hen. As the last young, a rubella bar hen was raised. Rubella hens were to be expected. Due to the genes of the father, but linked to Frosty. According to previous experience, such a pigeon should not have had a clearly lightened tail like this hen. The assumption goes back to a rubella cock as the biological father.

Fig. 12: Homozygous Frosty-Rubella cock and a Spread Rubella hen with offspring



Fig. 12a: Close-ups of the cocks of the first clutch from pairing 2: homozygous rubella + heterozygous Frosty, right the same plus Spread

The 3rd pair in Fig. 13 consists of a Rubella male and a diluted Frosty Rubella female. The cock comes from pure homing pigeons. The hen was raised from the initial pairing shown in Fig. 1 as grandparents and is therefore a sister of the female in pairing 1. Three females from pairing 3, two of which are shown, could be classified as hemizygous rubella without the Frosty factor. 2 checks and 1 barred cock met the expectations for earlier homozygous rubella cocks with heterozygosity for Frosty: The basic color is darker and the tail feathers less lightened than with rubella pigeons lacking Frosty.

Fig. 13: Pure rubella cock and a diluted Frosty Rubella hen with offspring

Surprisingly, three very reddish youngsters, of which the first cock is shown in close-up in Fig. 13a, with strikingly peppery wing and tail feathers. Possibly heterozygous dilution might be of importance, but the other cocks are also heterozygous dilute from the mother’s side. In the youngest of the three reddish individuals, the bars also are bleached, similar to homozygous Frosty cocks. Not clearly visible in the photo, but like the Rubella sibling in the nest, still long-colored, even if that was lost noticeably quickly after weaning.


Fig. 13a: Reddish cock of the 1st clutch from pair 3, homozygous rubella, heterozygous frosty, heterozygous dilution

The 4th pair in Fig. 14 consists of a wild-type blue homer, lacking other color genes as far is known, and a Frosty-Rubella hen. Blue and blue check ones would have been expected from this pairing without prior information, as Frosty and Rubella are considered recessive factors. Nevertheless, two young cocks who were heterozygous for the two factors from the mother’s side showed color deviations in the check pattern (Fig. 14a) and confirmed earlier findings. The contrast to blue check may be seen also in Fig. 14 by the blue check sisters. Another identical non frosty-rubella hen from the pair is not shown in the picture.

Fig. 14: Blue-bar homer (wild type) cock and Frosty Rubella hen with offspring



Fig. 14a: Wing shield of the check youngsters with a brownish tinge of the checks (in Fig. 14 the first and third young individual from the left)

Was nothing except expenses?

Discussions about frosty and rubella as rare factors will interest few pigeon fanciers. However, some of the findings could be of general relevance. From the point of view of inheritance mechanisms, the positive interaction of two non-allelic recessive factors is remarkable (Fig. 10, 11, 14a). Intermediate colorations and deviations from the wild type after mating two recessive factors should therefore not be interpreted as impartially as before as a sure sign of non-alleles. In the example, the effects are particularly noticeable in the case of cocks that are homozygous for both factors (Fig. 1). The example also shows that with the introduction of a blue-bar hen supposedly corresponding to the wild type, a hereditary factor may enter the strain which only shows its full effects in the following generations and can then trigger speculations about mutations. Many reported mutations will instead be modifications. The study is also an example of the fact that some questions could be solved, but also new ones such as the explanation of the color deviations in pairing 3. Not yet mentioned but a possible research project could be the observation previous to the parings discussed that the combination of Frosty and dilution seemed to cause problems with vitality in homozygous pigeons.


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

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