~ COLOR MODIFIERS ~

Let’s recap what we have learned so far, before we talk about modifiers. So far, we know that cock birds have two functional sex chromosomes and therefore they carry two out of three possible b locus pigments they are able to produce (red, black, brown). Hens on the other hand, only have one functional sex chromosomes (Z) and one empty sex chromosome (W), where there are no genes to be donated to the offspring from the empty sex chromosome. Therefore, hens only carry one b locus pigment on their only functional sex chromosome. Since hens only carry one fucntional sex chromosome, when referring to the sex-linked factors and hens, the term hemizygous is used to describe the arrangement where only one gene is present. Not all mutations are sex-linked; consequently a hen can be heterozygous for autosomal mutations such as beak crest, indigo, or barless pattern. This is where things can get confusing to many people. How could a hen be heterozygous if all female pigeons only have one functional sex chromosome?

All sex-linked mutations are on the sex chromosome and cocks have two of the functional sex chromosomes (ZZ) while hens only have one functional sex chromosome (ZW). However, what most of us tended to forget is that the sex chromosome is “not” the only chromosome in the bird. Hens, just as do cocks, have the normal double chromosomes for all the other chromosomes (autosomal). Therefore, it is very important to understand that “only” those mutations that happen on the sex chromosome are found singly in hens.

So far we know that b locus alleles (ash-red / wild-type / brown), reduced (rubella), dilute (pale / lemon), and almond (faded / frosty / qualmond / sandy / hickory), etc., are located in the sex-chromosome and therefore they are sex-linked. Every other mutation that we know has happened on one of the other chromosomes (autosomal chromosomes). Since the hen has two of each of those, she can thus carry something in a heterozygous state. Examples of some of these could be: dirty, crest, ember, slipper, check, barless, recessive red, spread, web foot, recessive white, etc. Just remember: Pigeons have three pigments; brown, blue/black, red. Brown is recessive to wild type; ash-red is dominant to wild type. All pigeons are one of these pigment types, though other modifiers and mutations may make it hard to see what the base pigment is. There are different mutations that modify the feather color of the bird and these mutations are located on a different locus and inherited independently from the b locus and its alleles. We do not know how many actual locus points there are on a chromosome yet.

In the case of recessive red, recessive opal, and recessive white, the b locus pigment production is modified. By that I mean, the b locus alleles stay the same in the genotype, but the new mutation located on other locus takes over and change what we “see” on the outside (phenotype). So, when these mutations present themselves, they conceal the pigmentation of the b locus (red, blue/black, brown). This condition is known as epistasis, where one gene suppresses the effects of another non-allelic gene. In other words, when two dominant genes are present but only one of them is expressed in the phenotype, then the gene that is expressed is said to be epistatic. So far, there isn’t any scientific research done to see what chemical changes takes place to change for example a red pigment found in ash-red mutation to appear as recessive red on the phonotype. Is it because these mutations add another layer of color to conceal b locus pigments? Do they change the feather structure completely and turn on/off the b locus pigment production all together? The answer is still unknown. Sometimes the pigments may be the same, but the new mutation changes the way it's laid down in the feathers.

Recessive red (genetic symbol e)

The recessive red only present itself in homozygous state (e//e). Otherwise, in heterozygous state, a pigeon just carries that gene in its genotype but does not show it in its phenotype. When the locus for recessive red has two copies of the same gene (e//e), the bird’s feather colors are modified and this bird would present itself as a recessive red. So, a recessive red hen still carries one of the three possible b locus pigments under that recessive red, however, we can’t see what she is carrying since it is modified by the recessive red gene. Same goes for the recessive red cock birds, where they still carry two out of three possible b locus pigments under that recessive red modifier. Just like recessive red, in the homozygous state a recessive yellow (the diluted version of the recessive red), a recessive white, and a recessive opal also modify the b locus pigments and not allow them to present themselves in the phenotype.

Under a microscope, the "red" pigment in ash-red and recessive red is still "red", but how it's laid down is totally different with both mutations. The fact of the matter is we don’t know exactly where in the pigment forming process the mutation interacts. When we have two different mutations interacting with the same pigment base (ash-red, and recessive red), and yet producing different results and being the result of mutations on totally different chromosomes is a mystery.

We know that recessive red is neither sex-linked nor dominant. Instead, it is a recessive autosomal mutation. Recessive red is also epistatic to many patterns, and many other mutations. Mutants are only rated vs wild-type to see if they are recessive or dominant to wild-type. However, there is another word in addition to dominant and recessive. The word is epistasis, which means that the particular mutation under discussion can hide other mutations which we would normally expect to see. However, it differs from dominance in that it is not on the same chromosome as the mutation it hides. Epistasis is used in two different ways. For example recessive white hides all other color mutants. Recessive white can correctly be said to be epistatic to all other color mutants.

The second way epistasis is used is a bit tricky. In this case wild-type can be epistatic to some mutant; however, this mutant can show only if some other mutant is present. An example would be white sides on recessive red. A recessive red white sides bird is a self red bird with white wing shields. Yet, if you simply replace the recessive red mutant with wild-type at that locus you will get a self blue bird with no white showing even when the mutant for white sides is homozygous. So wild-type is said to be epistatic to the white side mutant. White side is neither dominant, nor recessive, nor codominant. It simply does not show on an otherwise wild-type pigeon. There are other known examples where wild-type is epistatic to some mutant. The recessive red and recessive white pictures are submitted by Vahe' D'Ala. www.falconlofts.com

Recessive white (genetic symbol z^wh)

In the case of recessive white, what happens is that either the melanin is never produced or it doesn't get placed into the feather of the bird. Melanin is the pigment which is normally in a pigeon's feathers providing the colors we see depending on its shape and amount. Feathers of the bird grow normally, but, without melanin available to color it, only a white feather is produced. We actually see the feather as a white color because light hits the feather and bounces back to our eyes. Since none of the various light rays are absorbed by the melanin, all of them are bounced back and we see the combination of them as white. Recessive white plumage is often confused with albino mutation although they are two separate mutations caused by different genes. Separating these two phenotypes is actually quite easy when we take a close look at their eyes where albino pigeons have pink eyes and recessive white birds have bull eyes.

The bull eye is generally seen in recessive white and pied bald whites. All recessive white pigeons have bull eyes, white feathers, white beak, white skin and white nails. It's because just like the eye, rest of the phenotype genes for feather, beak, skin, and nail melanin production is turned off at the surface level. Because there is no melanin on the surface level, we see white. The bull eye therefore hides two additional genetic eye pigments under it, and does not allow us to see it since the melanin production on the outer iris of the eye is missing or not produced. Therefore, we can say that bull eye is epistatic to orange and white eyes.

Remember, recessive traits normally need two genes carrying that information to present itself on the phenotype of the bird. If a bird is homozygous for recessive white (z^wh//z^wh) then, no matter what color it would normally be, in every case, such a bird will be a white pigeon. That means a white bird can literally be almost anything genetically underneath those white feathers. It could be a blue-bar, a red check, a recessive red, a reduced T-pattern blue check, etc. The only way to find out what color a recessive white actually carries underneath those white feathers is to mate it with a blue bar, assuming that blue bar is not heterozygous for recessive white. All the offspring from this mating will be able to produce melanin in the offspring’s feathers which we can compare the mutation producing the pigments to our wild-type standard.

Recessive opal (genetic symbol o)

Just like recessive red and recessive white, the recessive opal is also an autosomal recessive mutation and is not sex-linked. The mutation was recognized as something unique and its inheritance worked out by W.F. Hollander in the 1930's. Recessive opal is very common in racing pigeons and there's a good amount of variation in coloring from bird to bird. Most have lightened tail and flight feathers. Their bars and checks are pinkish-bronze-grayish. A few birds are near-perfect mimics for Ash-reds. Ash-red gives a phenotype quite like homozgous red phase recessive opal. These are the ones which confuse people who believe they've produced ash-reds from a pair of blue birds. In reality, they have produced recessive opal that mimics the ash red. Because of this, sometimes they are even confused for reduced and dominant opal birds but they are two very separate mutations and each inherits independently of the other.

Diluted & Reduced

Diluted and reduced mutations also modify the color of the birds, they just don't conceal it the way recessive red, recessive white and recessive opal do.

We get cream bar (ash-yellow) from ash-red, dun from black, silver-dun from blue, recessive yellow from recessive red, and khaki from brown by a mutation called dilution. The dilution is located in a different locus (different forms of a gene at a particular physical location on a chromosome) and therefore inherited independently. Dilute is a sex-linked recessive mutation. Dilute is self descriptive and it does what it says… it dilutes the original pigment color giving us a faded version of that same color. Dilute gene is a recessive gene which can be carried but not shown for the cock birds, but if the hen has a single dilute gene in her sex chromosome donated by her father, then she will be showing the dilute factor in her phenotype. In order to raise a dilute cock, both parents must donate the gene to their offsprring. Hens can be raised showing dilute if her father carries a single factor (heterozygous for dilute) and if he donates it to his daughter. This also means that if a cock bird is homozygous for dilute, then all the female offspring from this cock will be diluted.

The dilution happens where the pigments on the feathers that absorbs the light to show the color is cut by half. Under the microscope, the pigment of an intense color like black and its dilute dun are exactly the same color (black) except that in the dilute there are smaller and fewer pigment granules, which creates appearance of another color--diluted black, known as dun.

There are for possibilities for dilute. D⁺ - Full color (not diluted), d^P - Pale, d - Dilute, and d^ex - Extreme Dilute

Remember that for a cock bird to be a diluted bird, he must be homozygous for dilute. I am not sure it was a coincidence or most diluted birds are hens, but I noticed after I posted the pictures that the first row of the following pictures are all cocks, and the second row showing the dilution is all hens. Click on each picture to make it bigger. In the pictures below, the dun female is actually the daughter of the black bird above her. How? Because this black bird is heterozygous for dilute. This means that chances of this cock bird producing a diluted hen offspring is 50%.

Reduced is different than diluted and has become a color in demand by many breeders and because of this, the quality of reduced birds are improved in many pigeon breeds. The reduced gene mutation was discovered in 1951 by Carl Graefe. He saw it in his rollers and recognized the difference. This was the beginning of the reduced gene as we know it today. Mr. Graefe, curious with this new color, proceeded to cross and backcross this color gene and perhaps because he was very knowledgeable breeder, we now have reduced genes in many pigeon breeds. It did not take him long to discover that it was a sex-linked dilution gene and recessive to the wild-type. He discovered that reduced will influence every color. "Pastel" is a word that best describes the influence of the reduced gene. Most breeders tend to prefer reduced mated with spread black. From this mating you would get reduced on black and it would look like a silver bird with the wing shield feathers laced with a black edge (lace).

These pictures on both sides are called rosy necks and they are more than likely reduced from a blue bar as we can see the tail band. Notice the beautiful rosy neck bars in the left bird, thanks to Dal M. Stone for putting this color into Birmingham Rollers. According to Mr. Stone, these birds are smoky reduced gimples although they mimic the appearance of dominant opal. The incomplete version of this bird would show pinkish neck and pink bars shown on the right and would make it easier for us the see the tail band.

Reduced is a single sex linked recessive gene but there is some hereditary problems associated with hens laying poor quality eggs which can affect hatchability. Unlike dilution where the pigment production cut by half, reduced seems to cut it by about a quarter. Reduced color changes a wild-type (blue bar) bird to gimpel opal (rosy neck) where it changes a dark red/green neck to whitish color. Reduced birds have a tendency to change quite a bit in the first molt and it might take a reduced bird a couple of molts to reach its true color. Dilute birds and reduced birds are short-downed and almost naked when they were first born but the short-down in reduced is usually nowhere near the shortness produced by dilute.

The three Color Reduction possibilities are: R⁺ - Nonreduced or Full Color, r - Reduced, r^ru - Rubella

Just like the dilute, the reduced is also a single sex-linked recessive gene. If you mate a reduced cock to reduced hen, all the young would be reduced. If you mate a reduced cock to any color hen, all the hens would be reduced and all the cocks would be a color-carrying reduced. If you mate any color cock to reduced hen, then all the young cocks would be a color-carrying reduced, and all the hens would be father’s color not carrying the reduced gene.

Phenotype vs Genotype

Recall from the previous pages that genotype is the term used to describe the genetic makeup, as distinguished from the physical appearance, of an organism. The genotype determines the hereditary potentials and limitations of an individual. Among organisms that reproduce sexually, an individual's genotype comprises the entire complex of genes inherited from both parents. Sexual reproduction guarantees that each individual has a unique genotype. Phenotype is the observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences. In other words, phenotype is the expression (the actual trait that we see) of a specific trait, such as "ash-red" color in pigeons. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two.

In the examples below, we will not cover all the sex-linked and all the autosomal mutations but instead only look at genotype and phenotype of two birds and we’ll only evaluate the sex linked b locus alleles reduced, dilute and autosomal recessive red mutations.

B^A - ash-red, B⁺ - for blue/black, b - brown
R⁺ - Nonreduced or Full Color, r - Reduced, r^ru - Rubella
D⁺ - Full color (not diluted), d^P - Pale, d - Dilute, and d^ex - Extreme Dilute
E⁺ - Full Color non recessive red, e - recessive red

GENOTYPE				PHENOTYPE
Sex Chromosome			Autosomal	This bird is a cock bird since he has two functional sex chromosomes. He is heterozygous wild-type (+) Blue/black split for brown (b). This bird also carries recessive red gene (e) but cannot express it in hererozygous state as he is a cock bird. He is non-reduced or full color (wild-type) but because the dilute locus carries two copies of the same gene, this bird is actually diluted from blue to dun.
b locus	Reduced	Dilute	Recessive red
+	R+	d	e
b	R+	d	-

GENOTYPE				PHENOTYPE
Sex Chromosome			Autosomal	This bird is a hen since she has 1 functional sex chromosome and 1 alleles for each sex-linked mutations. She is ash-red (BA), but because she carries two copies of the recessive red gene (e//e), she will present herself as a recessive red instead of ash-red. She has the wild-type gene on the reduce locus, but the dilute locus carries a copy of the dilute gene (d), so this bird will actually present herself as a recessive yellow.
b locus	Reduced	Dilute	Recessive red
BA	R+	d	e
-	-	-	e