Red Shoulder Yokohama

An Interesting Problem in Color Genetics


Brian Reeder

This paper presents data gathered to date on the genetic combination which is found in the color form known in the hobby as "red shoulder" and is seen only as a standard variety in the Yokohama.

The origin of the Red Shoulder Yokohama is obscure. They are said to descend from imports of Japanese Minohiki at the end of the 1800s. Hugo DeRoy is said to be the major person involved in the first Yokohama seen in Germany, which the RSY is said to directly descend from.

These first birds were proto-Onagadori-like longtails with pea combs and were white. Hugo DeRoy also had stunning Red Duckwing true Onagadori-like fowl at that early date. He found all these difficult to bred and outcrossed them with other birds to make stronger lines. These became the basis of the Phoenix and Jokohama of Germany.

The following fowl have been attributed to the ancestry of the Red Shoulder Yokohama, in addition to the above; Hamburg, Malay, Modern Gamefowl, Sultans, Brahmas, Mille Fleur D’Uccle and Pit Gamefowl.

The Red Shoulder Yokohama remained unknown in the US until the 1970s when they were imported from Germany. In America before that time, the Yokohama were more commonly gamefowl colored; the duckwings. These lines descended from American breeders who made their own Yokohama, with pea combs. White was also seen. However, the Red Shoulder is a different line, descending from the German import of Horst Schmudde.

In the thirty years these birds have been here, they have dwindled, and this is often blamed on the Americans outcrossing them. However, my experience would indicate a collection of deleterious factors associated with one or more of the many color and pattern genes involved in this very complex pattern, in addition to the long tail genes, which are detailed elsewhere.

We will establish the e-allele of this pattern and then show how the finished pattern is made by layering on pattern and color genes.

The E-allele of the Red Shoulder Yokohama

The red shoulder is occurring on e+, duckwing. This has been shown in e-allele testing and in test matings. When test mated to any e-allele, the behavior of the dimorphic segregation is always as per e+ in recombinant.

The S-allele

I have segregated from RSY S/S S/s+ s+/s+. The most wellcolored birds are s+/s+ which is then diluted (Di/Di), their coloring under the recombinant of genes being equivalent to a pale Light Brown Leghorn. The birds which are S/S often are very nice, but some of these show slightly lighter shoulders and breasts. Either will work, but the s+/s+ (with Di/Di Mh/Mh) allows for the ultra dark red shoulders and breast which are so desired.

Recombination Effects Creating the Basic Color Breaks

Let us put together what we have so far. This is then a Duckwing fowl, which is either silver, silver/gold heterozygote (in some males, but obviously, never in females) or red that is diluted to medium to light gold.

When diluted red or silver (or S/s+) are combined with Mahogany, you get he effect of the dark red shoulder, as Mahogany has the strongest effect on the shoulder (and breast when combined with Db). This allows for a pale hackled saddled bird to have a dark shoulder. The addition then of Dark Brown (often called ginger) Db, extends the mahogany into the breast. At this point, we have a bird with creamy hackle and saddle and wing triangle, with a dark red shoulder and a dark red breast (e+/e+ s+/s+ Di/Di Mh/Mh Db/Db), and a black tail with a black edging on the main wing feathers, making a line of black in the upper edge of the main flights when folded. The males hackle will show some striping at the lower hackle in the center of the feather, at this stage.

The hen is a dark breasted, dark shoulder and upper wing, all deep red, while the fluff is a light diluted golden, with a pale gold to creamy hackle. Her hackle is striped with a dark stripe running down the middle of each hackle feather. Her back at this point is stippled. She is typical of wild type, except for the areas of dilution and intensification of pheomelanin.

Both male and female have black retrices with black coverts that have a narrow margin of pale color in some of them.


It is clear that the pattern is based on "spangling," which is the gene combination seen in the Hamburgs called spangled. In other words, this is Db Pg Ml recombinant. This can be determined by the large size and tear drop shape of the spangle, which is typical of the homozygote of that recombinant. However, test mating has shown that mo, mottling, is also present, though it is not really necessary, as the Db Pg Ml recombinant does not require mo to make a spangle. However, I believe the presence of both the spangle linkage group and mottling is by chance; early breeders breeding in both genes, not knowing the difference genetically in the two forms, perhaps not even realizing they were different at all.

At this point, the birds will be as the male and female described above, but they will have the hackles melanized to various levels, most notably on the top of the head and with a distinctly widened stripe in the lower hackles. The saddling will show some melanization and heavier striping. The wing feathers will be melanized partially. On the breast, and in the shoulder, which is still dark red, you will now have tear drop shaped spangles, and in some cases, you will have the white tip of mo, mottling, showing up as well.

In the female, the breast and shoulder are as in the male, while the back is still stippled with a spangle and possibly a mottle too.

At this stage in both the male and female, the hackle will be melanized much as is seen in laced wyandottes or spangled hamburgs. This stage is e+/e+ s+/s+ Di/Di Db/Db Pg/Pg Ml/Ml mo/mo. Ideally, the birds have all the genes homozygous, though mo is not necessary and need not even be present, and segregations of many different kinds are seen with this wide group of genes amongst the RSY populations.

At this stage, we are nearly finished. We have a spangled Mahogany Dilute red duckwing, and in some instances, they will be mottled as well. We are nearly finished, as all we have to do is dilute this bird. However, the dilution of the RSY is perhaps the greatest mystery of this unique form.


The dilution effect seen in the Red Shoulder Yokohama is interesting and presents a challenge to understanding the process of melanin dilution. This factor dilutes both the eumelanin and the already diluted (Di) pheomelanin, turning both to white/near white. It is common in many RSY that the hackles or saddles show some level of creaminess. Those which are extremely white in hackle and saddle may be S silver at the s-allele or may have extra melanizers at work.

The dilution gene(s), when outcrossed to a non-diluted eumelanin, becomes a blue gray in the female in all eumelanin areas and is blue gray in the male with the tail growing out white at the base, with this factor often increasing over time. This is consistently the effect seen in F1 outcrosses of RSY to all the alternate alleles, when no form of eumelanin dilution is present.

This would then seem to indicate that Bl is present and perhaps the RSY is a "splash," as the f12 in outcross is not consistent with I/I+ Bl/bl+. However, the behavior of this "blue" appearing factor is not consistent with the gene Bl. I will present my results of test matings to show how this factor seems to work. I will not however try to present one specific answer for this problem factor, but will instead offer several possibilities that other researchers may in time pursue further.

In the most basic form, I believe that the RSY diluter (RSY~D) as seen in the exhibition form, is a homozygote for this dilution factor. However, whether this dilution factor is one straightforward DNA gene, a gene and some level of modification or modifiers that are combined and homozygous, that completely dilute the eumelanin and further dilute the Di diluted pheomelanin. I can not answer at this time what exactly is happening with the diluter factor. I think that only molecular testing could give us a definite answer.

The f1 as noted above of RSY x non-eumelanin dilution fowl, show a blue dilution of eumelanin, with males showing white in the retrices and coverts.

When the f1 x f1, there will be birds which are homozygous for the diluter, those which are blue-like (as per the f1 description), there are those which are non-blue or white, normal eumelanin, and thus seem to be homozygous for the absence of the diluter, but all the males of this type will grow some white in the bases of the retrices and the coverts. It is not an expected segregation pattern that the non-dilution males would all have the white base of feathers as described in the f1 blue like fowl.

Another interesting effect is that some of these birds, whether blue like or non-diluted with white in male tails, is that in both males and females, the amount of white may rapidly or slowly increase over the years, with each molt.

Very few birds in the generations beyond the f2 will not show the white in the tail feathers, and some level of progressive whitening over time. Is this then two genes? A diluter and a gene causing progressive whitening in the lower feather base? Or are we looking at one gene which is "splitting apart," losing codons and recombining in a new manner, each time becoming "diluted"? This defies my understanding of gene segregation, and would seem to indicate some factor which deserves further attention.

I will present the following possibilities where further research can perhaps determine the nature of this factor.

1. This could be a linkage factor between a "blue like" or even Bl blue, with a "dominant white like" or even I dominant white. These then would pass together.

2. This could be an unknown diluter, that mimics the effects of Bl in the heterozygous state, and mimics I/I in the homozygous state.

3. This could be two or more dilution factors in recombinant.

4. This could be an RNA modification of one or more genes for dilution, that shows wide penetration, depending on the homozygosity of the RNA factor(s).

I currently refer to this factor as RSY~D (Red Shoulder Yokohama Dilutor).


The combination of this diluter factor when fully expressed with the above outlined color and pattern combination, creates the phenotype of the RSY. This is then a fully eumelanically diluted Spangled Mahogany Dilute Ginger red duckwing. Thus you have a white to cream bird with a red breast and shoulder, which is spangled in white as well.

Deleterious Factors

The dilution factor as seen in the RSY would appear to be a deleterious gene, creating greatly weakened birds which often show great susceptibility to pathogens, possibly through a suppressed immune system or some other effect which weakens the birds overall physical health and vigor.

The nm non-molting genes and the Gt growth genes, which make the long tails, show deleterious factors as well. The growth factor Gt has a mild deleterious nature, while the nm non-molting genes shows possible highly deleterious effects, or a linkage to a highly deleterious factor.

It is my belief that the combination of the deleterious RSY~D factor with the nm and/or Gt factors, creates a more deleterious recombinant, making the RSY weak and lacking in vigor. The tight bottle-neck seen in all these birds, both in the US and Europe also presents the great likelihood of deleterious factors having been set. Linkage patterns and/or pleiotropy may be at work. Further research is needed to determine both the deleterious factors present and the nature of the dilution factor in the RSY.



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