Advanced Color Genetics - Why the colors work the way they do
If you've made it this far, you must have grasped the basic concepts of Gouldian genetics thus far. Now you're probably asking - "What else is there to know? Why/How do the genetics work the way they do? What is the deeper explanation?" Hopefully I can paint a better picture on this page of how the colors actually work to produce the gouldian mutations existing today.
First - let's try to understand the different pigments that make up the color present on the Gouldian's body to begin with.
There are five basic colors to speak of:
Being a "structural" color means that the blue color we see (on a blue bodied bird, for example) is the result of wavelengths from the red end of the color spectrum being absorbed by the feathers, whereas blue is reflected back to our eyes - being the color we see.
The two melanins are: Eumelanin and Phaeomelanin. Eumelanin is responsible for black pigmentation, where Phaeomelanin is responsible for Reddish-Brown pigmentation.
In describing the mutations that exist today, what it boils down to is the manipulation of the bird's ability to express these different pigment groups. We are altering the way a normal bird can express color - not creating new color components themselves.
The Different Body Color Mutations, and How They Were Derived
Birds that lack eumelanin (black pigment) are Dilute bodied birds. However, because Dilute bodied birds only have one copy of the yellow gene, which is co-dominant, the remaining genes responsible for wild type body color can still express a portion of dark coloration, leaving the black normally present on birds as a dull grey or smokey color instead. If the cock is DF for yellow, it can't produce any eumelanin at all, and this is why the black on these birds appears off-white or cream colored. The exception is SF Cocks who are also white breasted. The exact explanation for this is not fully understood, but it suggests some sort of relationship between breast and body color inheritance. White breast is due to the inability to produce either melanins - so it stands to reason that perhaps a yellow bird with a white breast has a difficult time producing ANY melanins, and thus appears yellow all over. But I digress.
A bird that only lacks Canthaxanthin results in a Yellow head bird (recessive).
In a yellow bodied bird - Eumelanin and Phaeomelanin both can not be produced. In this case as well, green body color is erased because the structural blue is masked by yellow.
In a blue bodied bird - neither carotenoid colors (lutein or canthaxanthin) can be produced, creating a blue bodied bird by default. Remember - blue body color is not produced by food synthesis, it is purely the result of feather structure. This explains why genetically red head blue bodied birds do not fully express the red head color (although why it is not completely subdued I am not sure) but instead appear anywhere from salmon to beige in color.
In a silver bodied bird - we have an interesting situation. We are essentially combining the characteristics of a yellow bird with those of a blue bird. This results in a bird that is not able to produce either melanin or carotenoids. No melanins mean no black, and no carotenoids mean no red or yellow. However, the yellow prevents the structural blue from showing up as well - so we're left with a bird that is hardly capable of producing any color at all and appears as off-white or silvery in coloration.
Because head and breast colors are, for the most part, inherited independently - these are not affected and remain untouched unless controlled by selective breeding. E.g., in order to produce an "all-white" bird, one would need to selectively produce a Black Head, White Breast, silver bird. We know that yellow prevents the expression of the eumelanin responsible for the black head, and below you will see that the lack of either melanins is what results in a white breasted bird.
An easy way to look at body color, for me, is to think of a color palette. Many of you may remember from childhood art classes that Blue + Yellow = Green.
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