2.4 Color Genetics
The color genetics that we are about to discuss applies to budgies, lovebirds, Indian ringnecks, Alexandrines even cockatiels (think of the Whiteface mutation in cockatiels as the "blue" Cockatiel). Blue is always recessive in all these species. Our focus will however remain on budgerigars.
Sometimes a gene in the DNA causes the production of psittacine (yellow pigment) to completely stop. The gene that stops the production of the yellow coloration is called the blue gene. When two copies of the blue gene are present (BB) no yellow color is produced while the blue color is produced normally. This causes the bird to appear blue with a whiteface.
We already know that a bird with only one copy of the blue gene (GB) appears normal green as the production of the yellow pigment is not stopped.
Another type of blue gene also exists. This blue gene does not completely block the production of the yellow pigment but reduces it significantly. The yellow pigment is no longer produced in the body but some is still produced around the face area. Such a bird appear to have a yellow face with a blue body. (see fig 3).
In ringnecks, alexandrines and lovebirds when the production of the yellow color is only partly blocked we call this mutation turquoise. In Cockatiels we call this mutation Creamface. Generally this mutation is known as par-blue.
Let us now introduce the ino gene. We will study the ino gene in greater detail when we discuss sex-linked mutations. The ino gene acts to stop the production of Melanin which is responsible for the blue and black coloration in budgerigars. This causes the bird to appear yellow. (see fig 4) Such a bird is called a lutino. The eye of such a bird appear red as there is no black pigment produced in the birds eye. The red coloration is produced by the reflection of the blood vessels.
Finally, if a bird has both the ino and the blue genes it is unable to produce the yellow and the blue/black colors. Such a bird appears to be white and is called an albino. It is very important to understand here that there is no single Albino gene. The albino is a combination of the blue and the ino genes. (see fig 5).
To summarize, budgies produce 2 types of pigments, psittacine (yellow) and melanin (blue/black). The blue gene blocks (partially or completely) the production of psittacine, the ino gene blocks the production of melanin. The combination of these genes is responsible for the five colors we have discussed above.
I have intentionally left out one combination of mutations in the above examples. What is that combination and what is the bird called?