Genetics of Dilution

Summary:
Normal - dominant
Greywing - recessive, co-dominant with clearwing
Clearwing - recessive, co-dominant with greywing
Dilute - recessive

There are four dilution alleles: normal, greywing, clearwing, and dilute. The normal allele is dominant to all other alleles. Greywing and clearwing are both recessive to normal and dominant to dilute. Greywing and clearwing are co-dominant with each other, which means they do not completely dominate over each other and both affect the budgie's phenotype when present. Dilute is recessive to all other alleles.

The dilute mutation can be confusing since there are three non-normal alleles which make four different phenotypes. This is how it works: Greywing and clearwing are co-dominant. The greywing gene by itself produces more pigment in the wings, causing the grey colored markings, and less pigment in the body feathers, causing 50% color dilution. The clearwing gene by itself produces less pigment in the wings, causing very light markings, and more pigment in the body feathers, causing the bright body color. When a budgie has both a greywing and a clearwing gene, the budgie is a full-body-color greywing. The greywing gene makes up for the lack of wing pigmentation ability of the clearwing gene, and the clearwing gene makes up for the lack of body feather pigmentation ability of the greywing gene.
So when a budgie is homozygous greywing or has a greywing gene with the recessive dilute gene, the budgie has the grey wing markings and diluted body color. When a budgie is homozygous clearwing or has the clearwing gene with the recessive dilute gene, the budgie has very light wing markings and a bright body color. When a budgie has both the greywing and clearwing gene, it is a full-body-color greywing with grey wing markings and bright body color. When a budgie has two of the recessive dilute genes it shows the traits of dilute with about 70% washed out markings/color all over.

Here, "C" represents the normal gene, "c^g" represents the greywing gene, "c^w" represents the clearwing gene, and "c^d" represents the dilute gene. With these four alleles we have the following possible genotypes:

• CC, Cc^g, Cc^w, Cc^d - Two normal genes or one normal gene and any of the recessive genes, resulting in a normal budgie.
• c^gc^g, c^gc^d - Two greywing genes or one greywing gene and a dilute gene, resulting in a greywing budgie.
• c^gc^w - One greywing gene and one clearwing gene, resulting in a full-body-color greywing budgie.
• c^wc^w, c^wc^d - Two clearwing genes or one clearwing gene and one dilute gene, resulting in a clearwing budgie.
• c^dc^d - Two dilute genes, resulting in a dilute budgie.

As you can see there are only five phenotype possibilities but many possible genetic combinations. It is key to remember that greywing and clearwing are co-dominant. The normal greywing has grey marking and 50% body color dilution. The normal clearwing has very light markings and no body color dilution. When the greywing and the clearwing gene are both present, we get the full-body-color greywing, which has the grey markings of the greywing mutation and the body color of the clearwing mutation. Other than the co-dominant relationship between greywing and clearwing, all other combinations work in a dominant-recessive relationship. The normal gene will prevail in the presence of any of the other recessive alleles. The greywing gene prevails when the dilute gene is present. The clearwing gene prevails when the dilute gene is present. Only when both genes are dilute does the dilute phenotype show up since dilute is recessive to all the other alleles. Below are Punnet square examples of some possible pairings. From these you can see that breeding the different dilution varieties can get pretty complicated.