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V.  Domestic and Muscovy Duck genes and comments

It is believed that the ancestor of all modern domestic ducks is the common mallard. The genes carried by the mallard are considered to be the 'wild-type' and are distinguished from other genes (mutations) by the superscript '+'.

Mallard ducks are Anas platyrhynchos and muscovy ducks are Cairina moschata. Being genetically dissimilar (mallards (and domestic ducks) belong to different genera and species than do Muscovy ducks) the genetics are given separately because the wild-type (which is the 'reference' for all the genes) is different in the two fowl. Some fowl of different genera do hybridize and this is the case with Muscovy and Domestic ducks. (In addition, pheasants will hybridize with chickens and turkeys Crawford,Ch. 15.) The Muscovy x domestic duck is the cross used for commercial meat production. Usually offspring from trans genera crosses such as this one are not fertile but occasionally they are.

The discussion of poultry genetics in these pages is relevant to the ducks except for when specific genes for other poultry are being considered (for example, the sex-linked traits function the same as they do in chickens). Below is a table of genes and gene symbols specific to the domestic ducks.

Because there are strong interactions between the black dilution genes (such as the sex-linked brown dilution and autosomal blue dilution) and the genes that are allelic at the E-locus (extended black, E, and the wild-type, e+), I have added a separate table after the gene tables of the domestic duck to clarify these interactions.  I have tried to incorporate relevant and interesting comments about these genes in the comment section. I continue to update this and correct it....

 

Domestic Duck Genes of Common Interest
Sex-Linked Genes Symbol
Comments
Brown dilution d Recessive. The main effect is to dilute the black pigment (eumelanin) changing it to a chocolate brown. Brown and blue dilution can work together giving an even lighter bird.
Buff dilution bu Recessive. Lightens bill, feathers, legs and feet.

Autosomal Genes
Autosomal Genes Symbol
Comments
Mallard M+ Dominant to dusky (md) but recessive to restricted (mallard), MR. Allows expression of wild-type plumage coloration. Breed examples are Rouen and Brown (grey) Call.
Restricted (mallard) MR Dominant. Basically a modified mallard pattern with white on the wing fronts at maturity. Breed examples are Silver Appleyard and Pekin.
Dusky md Recessive. Allelic to mallard and restricted and recessive to both. The dusky pattern is darker and plainer than the mallard both in the day-old and adult. Breed examples are Khaki Campbell and Buff Orpington
Dark phase Li+ Dominant. This gene is the wild-type gene present in the mallard and the Rouen breed. It allows full expression of the three alleles of the M+ locus.
Light phase li Recessive to the wild-type and dominant to the harlequin phase and allelic to both. Characterized by a lightening of the feathers and replacement of some by white. Extends the claret-colored breast of the male.
Harlequin phase lih Recessive and allelic to both the dark phase and the light phase. The effects on plumage color are similar to the light phase but more exaggerated.
Extended black E Dominant. Causes solid black pigment to be laid down in all areas except those influenced by genes for white spotting. Typical of the Black Orpington, Black Cayuga and Black East Indian. Evidence exists suggesting that extended black influences eggshell color giving it a grey tint.
Blue dilution Bl Incompletely dominant. Bl is primarily a diluter of eumelanin (black pigment) and therefore it's function is highly influence by whether the fowl has the E or e+ gene. The heterozygotes can be a blue-grey while homozygotes can be nearly white.
Recessive white c Recessive. This gene is responsible for the white in common white breeds. In the homozygous state, recessive white masks all other color genes.
Dominant bib S Dominant. White on upper neck and breast. This may be an interaction effect and not really a gene. Expression is variable.
Recessive bib b Recessive. Causes fowl to have a bib of white.
White primary w Recessive. A breed characteristic of Blue Swedish. The gene causes one or more primary feathers to be white.
Runner pattern R Incompletely dominant. The runner pattern is a complicated arrangement of white markings on a colored background found typically in the Fawn and White Indian Runner ducks. The expression of the gene is sensitive to (unknown) modifying genes.
Magpie pattern - Not a real gene. The magpie pattern results when the dominant bib, S, is present with (homozygous) runner gene, R.
White bill and skin Y Characteristic of the Aylesbury. Causes skin and bill to be pink or white.
Hooked bill no symbol The bill curves downwardly.
Eggshell color G+ The buff-green color of the wild mallard eggshell. The genes responsible for the blue/green and white eggshell colors had not been investigated as of 1990.
Crest Cr Incompletely dominant and lethal in homozygous state.

The table immediately below is intended to help the interested reader know the way in which the blue and brown dilution genes interact with the E and e+ genes. Since the blue and brown dilution genes act on the black pigment (eumelanin) it is important to their expression that there be some black pigment.

Digressing just a moment. Please recall that the superscript '+' denotes the wild-type gene. So, for example, the e+ gene is the genetic code for the wild-type coloration that stems from the E-locus. Similarly, the D+ gene is the lack of the recessive brown dilution genetic factor, which is also the gene possessed by the wild-type (mallard) fowl. Analogously, the bl+ wild-type (mallard) recessive gene is the lack of the dominant blue dilution factor. Something that I feel is confusing to a lot of people about poultry genetics is that all the genes are referenced to the wild-type gene and for every gene location on every chromosome there is a wild-type gene there except when we specify the existance of a non-wild-type gene. So for every gene in the gene tables there is a corresponding wild-type gene (which will have the superscript '+'). We usually just assume this and don't list the wild-type genes in the tables unless some special point is being made about them. So the philosophy that one should have is that you're starting out with the wild type bird and changing genes (from the wild-type to whatever you want)and the difference between the bird you get and the wild-type is the result of the gene changes you made.

An example mating that might make use of the table immediately below is the mating between a black female having the genotype E/e+ D+/- with a chocolate male having genotype E/e+ d/d. To start off, one could make two Punnett squares, one for the inheritance of the sex-linked brown dilution and the other for the inheritance of the E-locus genes.

The first Punnett square would have the two 'd' genes on the left side (I like to put the males there) and the female genes go on top and they are D+ and the dash (indicating her W chromosome is lacking a location for brown dilution gene). The Punnett square below represents the inheritance of these genes:

This Punnett square gives 50% males with genotype D+/d and 50% females (the ones that inherit the dashes or W chromosome) with genotype d/-. So, none of the males will be chocolate because 'd' is recessive and the females will be brown.

The other Punnett square will have E and e+ along the left side as well as the top.

This predicts 50% E/e+, 25% E/E and 25% e+/e+.

Now, since every breeding outcome predicted by the first Punnett square can occur with every breeding outcome of the second Punnett square, one has to take each prediction of the first square with each prediction of the second square and check the table below for the phenotypes. When you do that, multiply the percentages as well. So, for example, from this mating there will be 25% D+/d E/e+, 12.5% D+/d E/E, 12.5% D+/d e+/e+, 25% d/- E/e+, 12.5% d/- E/E, and 12.5% d/- e+/e+.

Since no mention of the blue dilution was made, the table entries below for the lack of Bl are relevant. The lack of the Bl gene is the bl+ gene since the wild-type gene must occupy that location on the chromosome if Bl doesn't. With these dilution factors it is common for the heterozygotes to have a similar effect as the homozygotes only not as strongly. This is not always true, however. In the case of the E/e+ heterozygotes, it is reasonable, since extended black is dominant, for the heterozygote to look more like the E/E homozygote.

Interactions of diluters and E-locus genes
Dilution genotype Combined with E/E Breed examples Combined with e+/e+ Breed examples
Bl/bl+ D+/D+ blue-grey Blue Swedish, Blue Orpingtonblack areas of wild-type diluted to blue-greyApricot Call, Saxony
Bl/Bl D+/D+ blue-splashed white lighter colorations of Blue Swedish, Blue Orpington black areas of wild-type diluted to lighter version of blue-greyApricot Call, Saxony
bl+/bl+ d/d uniform chocolate Chocolate Orpington, Chocolate Indian Runnerblack areas of wild-type diluted to chocolate brownApricot Call, Saxony
Bl/bl+ d/d Light blue with some pink shading (lilac) nonebuffBuff Orpington
Bl/Bl d/d lilac-splashed white nonepale bufflighter Buff Orpington

Some Genetics of the Muscovy Ducks

By 1990 only ten plumage color genes had been illucidated genetically. More are known to breeders, but they have not been genetically characterized. Below is a table of genes which are, I believe, reliably and scientifically characterized.

Muscovy Duck Genes of Common Interest
Sex-Linked Genes Symbol
Comments
Chocolate ch Recessive. All black pigment is replaced by brown and red is unchanged.

Autosomal Genes Symbol
Comments
Atipico / dusky a Recessive. There are possibly two variants of this gene. The wild-type pattern is replaced by a brown color in the duckling. Some adults may show a bib. The brown coloration of the down does not persist into adulthood.
Barring b Recessive. Causes bars to occur on pigmented feathers. It also expresses in down. It influences the color of the beak (making it lighter). Barring is present in black plumage as well as that having the blue dilution.
Brown-rippled br Recessive. Ducklings have brown down, beaks and feet. The 'rippled' aspect of this gene causes a barring pattern. There is no difference in the barring between the sexes. The gene will express in the presence of lavender, atipico and piebald. Birds that have both barring, b, and brown-rippled, br, have been produced.
Blue dilution N Incompletely dominant. The heterozygote is blue and the homozygote is more grey. The bill and feet colors are diluted.
Lavender l Recessive. A diluter of both red (pheomelanin) and black (eumelanin) pigmentation. Adults are a lavender-grey in color.
Sepia, faiogeno f Recessive. A dilutor of both red and black pigment. Influences skin color. The cuckling is khaki-colored with pink beak and yellow feet. Adults are sepia with beetle-green sheen. There is much variation in the coloration of adults. This gene is thought to be rare in North America.
Self-white P Dominant. The homozygote is white, the heterozygote is black and white speckled.
Duclair piebald d Recessive. The homozygote is a white bird with black on the head, back saddle and tail. Adults may have a small white bib.
White head, canizie C Dominant. Causes head and part of the neck to be white.
Snow-white down no symbol Not much is known about this gene other than it exists.