Clearwing Budgerigar Mutation - Genetics

Genetics

The Clearwing mutation is one of the few that affect different areas of the body selectively. Like many budgerigar mutations, it is the black melanin pigment that is affected. This pigment is present in the medulla or inner cells of the barbs of all the feathers which appear green (or blue in the white series), and in the cortex or outer cells of the barbs of all the feathers which appear black. The Clearwing mutation causes a large reduction in the number of pigment granules in the cortex, but only a very small reduction in the number of pigment granules in the medulla.

Since the black markings in the budgerigar are due mainly to melanin pigment in the cortex it is these areas that are most affected by the Clearwing mutation, while the intensity of the blue colouration, which is dependent on pigmentation in the medulla, is affected very little.

So the Clearwing mutation exerts a selective effect, not on the wing feathers per se, but on cortical pigmentation. In this respect it is the opposite of the several Clearbody budgerigar mutations, which seem to selectively suppress medullary pigmentation while leaving cortical pigmentation unaffected.

The Clearwing is an autosomal mutation of the dil locus given the symbol dilcw, and so is a member of the multiple allelic series which also includes the Dilute (dild) and Greywing (dilgw) mutations. The Clearwing allele is recessive to the wild-type, dominant to the Dilute allele and co-dominant with the Greywing allele.

The effect of the Clearwing mutation is fully visible only in a bird which is homozygous for the Clearwing allele with the genotype dilcw/dilcw or is heterozygous with the Dilute allele, with genotype dilcw/dild. When heterozygous with the wild-type allele with the genotype dil+/dilcw the phenotype is identical to the wild-type Light Green and the bird is known as a split Clearwing.

When the Clearwing and Greywing alleles are both present the genotype is dilcw/dilgw and the bird is known as a Full-bodied Greywing. Both alleles are partially expressed, giving the bird wings like a Greywing and a body colour like a Clearwing. A more detailed description is given under the Greywing mutation.