Had a nice chat with at the 2016 Ohio Nationals about silver genetics in d'uccles and improving some descendants of a project silver mille fleur d'uccle line. It brought up some interesting questions about how to brighten the white without losing the chevrons and spangles. So of course I had to go research the genes involved since I plan on working with this line.
Some background on Silver:
Silver (S) is a partially dominant gene on the Z sex chromosome (remember sex chromosomes are ZZ for male, ZW for female). Roosters can carry two silver alleles, one on each Z chromosome. Hens can only carry one silver allele since they only have one Z chromosome.
Simplistically, non-silver birds are “gold” (s), the more common “wildtype” appearance. For example, a normal mille fleur rooster has two copies of s instead of S, and a mille fleur hen has one copy of s.
That means a silver rooster may be Ss, which yields a yellowish color. An SS rooster should be pristine white. However, leakage issues can make for a yellow bird in males AND females.
Because silver is a sex-linked gene, a silver hen will always have only one copy of silver and will always throw her one silver gene to her male offspring.
That's something to consider in crossing— whether it’s better to use a rooster that may be split silver (Ss) rather than a silver hen. Roosters can only donate Z sex chromosomes. The hen donates her Z to make a ZZ male chick, or her W to make a ZW female chick. Remember that her W chromosome doesn’t carry the silver gene, so neither will any of her daughters!
In other words, if you cross a mille fleur rooster to your silver hen, it will give you 100% mille fleur pullets and 100% split silver cockerels (Ss).
On the other hand, if you cross a Ss rooster to a mille fleur hen, you will get 50% silver pullets (the other 50% will be mille fleur pullets) and 50% Ss cockerels (the other 50% will be mille fleur cockerels).
Either way, you’re getting only split silver males.
If you have to cross colors, ideally you’ll use a homozygous silver (SS) rooster with a mille fleur (ss) hen to get 100% silver pullets, 100% Ss cockerels.
Getting back to the point, it seems likely that the silver roosters out there today are all homozygous by now (unless someone has been crossing colors). That means if we have yellowish silver mille fleurs, its likely leakage, especially if the hens are the same yellow shade as their rooster siblings. I discussed crossing silver mille fleur d'uccles to white d'uccles to brighten them, an idea that a well-respected breeder suggested.
Here's some background on white genes:
There are two main types of white: dominant white, and recessive white. You might consider silver also a type of white.
Silver affects ONLY red pigments.
Dominant white affects ONLY black pigments.
Recessive white affects both red and black based pigments.
Example: take a mille fleur, add silver allele, and all red areas turn white, leaving chevrons and spangles intact.
Take a mille fleur, add a dominant white allele, and you get golden necks, turning the black spangles white. Take a solid black bird, add dominant white, you get a white bird. All black pigments turn white.
Take any color bird, add two copies of recessive white, and you should get a completely white bird (there may be some leakage issues, not sure).
Renowned Dutch poultry geneticist, Henk Meijers, the creator of the Chicken Genetics Calculator tool, claims that most "White" birds are genetically recessive white (not black birds with dominant white gene).
Our goal is to brighten only the white areas of a silver bird, so we wouldn't want to cross silver to a dominant white bird like a golden neck, nor a black-based white bird, or it would erase our spangles.
Assuming you've found a true recessive white to cross to, there are two problems.
If you cross recessive white (cc, ss) rooster to your silver (CC, S-) hen, it will give you 100% non-silver, non-recessive white (Cc, SS) pullets and 100% split silver, split recessive white cockerels (Cc Ss).
If you cross your homozygous silver (CC, SS) rooster with a recessive white (cc, s-) hen, you'll get 100% silver, split rec. white (Cc, s-) pullets, and 100% split silver, split rec. white (Cc, Ss) cockerels.
The first problem is that most of the offspring from these F1 crosses will be split recessive white, and recessive white shouldn't show through at all unless a bird has two copies of it. One copy of recessive white itself will not improve the whiteness of the usual silver or split silver, but two copies will turn your bird completely white.
As for the rest of the offspring, what exactly is a non-silver mille fleur, non-recessive white bird? It’s essentially as if you crossed a gold mille fleur with whatever color is hiding beneath your white bird.
So what is hiding beneath your recessive white? It could be any color, with or without spangles or chevrons, and perhaps even with dominant white also thrown in. For our purposes, the best we can hope for is a very pale mille fleur. Even if it is a mille fleur, it's gone generations without any selection on the quality of its spangles or chevrons or buff base color, because all of that was masked by white. This means that your F1 generation may be a huge step back in spangle quality and color correctness!
So now we know that adding white genes themselves won't directly brighten silver, and could even make it worse depending on what other genes are masked by your white birds. It seems like a dead end. But what other benefits might there be in crossing to white?
Leakage genes are not well understood. It's possible that crossing to different lines with less leakage genes, regardless of color, can help. Of all the d'uccle colors, whites are highly likely to have leakage genes bred out of them since that is what they are selected for. Whether your whites are dominant white (black bird underneath) or recessive white (any color underneath) crossing to them will sacrifice some of the silver mille fleur color correctness for a few generations in order to get that decrease in leakage genes from the white lines.
The more traditional way to go about brightening silver is to consistently breed only the lightest silvers every generation, essentially decreasing leakage genes and/or lightening the underlying buff color. Or if you must cross (for spangle improvement), choose a mille fleur with the lightest buff possible so that the appearance of leakage will be minimal. Fingers crossed that you will get lucky and hatch some super pale birds quickly!
This is a case where importing clean euro silvers and then breeding to APA/ABA type would jump this project forward by generations.
Some alternate ideas are to breed in dilution genes Di (Dilute), Cb (Champagne Blond), or ig (inhibitor of gold, aka cream, aka lemon) in addition to silver. These genes would dilute the underlying buff color to make leakage less apparent rather than targeting leakage genes directly. However, some of these dilute genes would have to come from crossing to another breed. If we are going to do that, we may as well also look into crossing to other breeds that already have clean silvers and improve d’uccle type and silver mille fleur color from there.
Keep in mind, the strategies above are based off of an evolving concept and the information may change as we learn more. The more people working on this in different ways from different angles, the faster silver breeders and silvers will benefit, so feel free to chime in with your ideas and results. Thank you to everyone who contributed in the discussion following the first draft of this article on our group's Facebook page.
For more poultry genetics info and access to the Chicken Genetics Calculator, see:
Genetics of Chicken Colors and Basics