The Clearwing budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Clearwing variety, often known as Yellowwings in the green series and Whitewings in the blue series. When combined with the Greywing mutation the variety is known as the Full-bodied Greywing. When combined with the Yellowface II and Opaline mutations the Rainbow variety is produced.
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Appearance
The Clearwing Light Green has green body feathers only very slightly paler than the normal or wild-type Light Green with highly contrasting yellow wings. The Clearwing Skyblue is similar but with a blue body and white wings. The body colour is a little brighter in tone than the corresponding normal.
The wings and mask carry pale grey shadows of the normal markings and spots. In the best show birds these are quite faint, but nevertheless are still clearly visible. The cheek flash, cere and eye are unaffected by this mutation. The long tail feathers are much paler than the wild-type, being smokey-grey in the blue series and a pale grey-green in the green series. Clearwings which are split for Dilute are often slightly paler than pure Clearwings.
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.