The Single-Factor Clearwing

© Pantcho Tomas 2001

Among Australian Clearwing breeders, the expressions single-factor and double-factor Clearwing are rarely used. In fact, many believe that such birds do not exist. Certainly, when viewing Clearwings there appear to be no justifiable differences as for example in Australian Goldenfaces, or in the Spangle variety. The expressions have been coined to describe geno-type (genetic type) rather than pheno-type (visual appearance).

A double-factor Clearwing is a pure breeding Clearwing and possesses 2 Clearwing genes, one on each of its homologous chromosomes; that is, one inherited from each of its parents. They are sometimes denoted df or 2-F. By comparison, a single-factor Clearwing, sometimes denoted sf or 1-F, possesses only one Clearwing gene. .The corresponding gene locus (position on the second homologous chromosome) may be occupied by a Dilute gene or a Greywing gene

Yellow Or White Gene Specific

While a composite Greywing-Clearwing (Full Body-coloured Greywing) may be thought of a single-factor Clearwing, current overseas breeders seem to have adopted a usage specific to the Dilute. Thus a single-factor Clearwing, according to modern usage, is visually a Clearwing but split for Yellow or White (ie Dilute). There appear to be two pheno-types of the Dilute, that is the heavily suffused variant (called a dilute Greywing by some) and the lightly suffused variant (the Cinnamon-free Black-eyed Self). Hence, there are two different geno-types of the single-factor Clearwing, a point often overlooked. It must be stressed that the heavily suffused Dilute is not a diluted Greywing or what was once called a 50% or "50-50" Greywing.

Among those who accept that single-factor and double-factor Clearwings exist, there is a general concensus that double-factor Clearwings can be identified as those with the clearest wings. This has some justification, and is sometimes correct, but exceptional wing clarity is also a characteristic of single-factor Clearwings. Double-factor Clearwings in many cases do have exceptionally clear wings, but this is usually the result of continually pairing together two Clearwings, and selecting pairings for exceptionally clear wings.

Composite Recessive And Dominant Characteristics

In a previous edition of this magazine it was suggested by a prominent Clearwing breeder of many years, that a composite Clearwing Spangle was a single-factor Clearwing. By definition, this may not be strictly correct. A Clearwing Spangle may also be a double-factor Clearwing, and still exhibit Spangle features.

Perhaps the most difficult concept to grasp among budgerigar breeders is how both a recessive characteristic and a dominant characteristic can appear in the one bird. This clearly shows a poor comprehension of genetics, and how genes work. Genes for each mutation have a discrete gene locus (location) on their homologous chromosome pairs. Hence, just as it is possible to have Clearwings with dominant or recessive colours and dominant colour modifiers (dark-factor, violet-factor or grey-factor) it is also possible for them to exhibit dominant variety characteristics such as Spangle or Dominant Pied. The gene loci for these mutations, are at different positions on the chromosome pairs to those for Clearwing.

Among the recessive varieties, the Greywing, Clearwing, and the two types of Dilute have genes which can occupy the same gene loci. That is why they are referred to as multiple allelomorphs, or multiple alleles for short. They were caused by different mutations of the same gene. All budgerigar mutations may be referred to as alleles of the wild-type budgerigar, but not all are multiple alleles. It follows that a Normal may be split for only one of these. Any composite involving two of these multiple alleles cannot be split for a third in the series, as all birds only carry two of all non-sex-linked genes.

The other recessive varieties, for example the Recessive Pied, or the German Fallow, have genes located at other discrete gene loci. Therefore to have a Clearwing Recessive Pied still requires two genes for the Recessive Pied mutation. The same applies to the visual Clearwing Fallow. This requires two Fallow genes, but may still be split for Dilute. Pair a Clearwing to a Fallow and in most cases you get a nest full of Normals, all split for both Clearwing and Fallow. These are referred to as double splits among other groups of bird fanciers. If the Fallow is already split for Clearwing or alternatively Dilute, then a Clearwing can occur in the nest. This may be baffling to some and lead to the belief that the Fallow is a multiple allele of the Clearwing. There is a significant body of evidence to show that it is not.

Perpetuating Single-Factor Clearwings

To the majority of Clearwing breeders, whether a Clearwing is single-factor or double-factor is irrelevant information. This is because they constantly pair Clearwing to Clearwing, and have done so for many years. Any variation, or apparition, is immediately culled and often forgotten about. Using this philosophy, many now claim that their Clearwings are not split for Dilute, hence cannot be single-factor. However, I have been able to prove that most are wrong in this assumption, by producing Dilutes from supposed pure breeding Clearwings.

If the Dilute gene is present in just one Clearwing this can be perpetuated for many generations without showing up. It is also surprising to find that many Clearwing studs are also carrying the Fallow gene. Nevertheless, when a double-factor Clearwing is paired to a single-factor Clearwing, the theoretical expectation is as follows:

sf Clearwing * df Clearwing = 50% sf Clearwing + 50% df Clearwing (1)

With this type of pairing, there is no guarantee that the chicks with the clearest wings are double-factor. Variability among the progeny can be attributed to the action of various secondary modifier genes. When two single-factor Clearwings are paired together, 25% of the progeny will be Dilutes, as in the following theoretical expectation.

sf Clearwing * sf Clearwing = 25% df Clearwing + 50% sf Clearwing + 25% Dilute (2)

In this type of pairing, if one of the parents is split for suffused Dilute, then the Dilute youngsters will be heavily suffused with body colour. These are occasionally referred to as dilute Greywings or sometimes dilute Clearwings. If the Clearwing parents are both split for the lightly suffused Dilute (the cinnamon-free Black-eyed Self) then the Dilutes will look like a Cinnamon-free Black-eyed Self, or a lightly suffused Yellow or White free of wing markings. These are sometimes called dilute Clearwings.

The various names used for these non-clearwing progeny vary from breeder to breeder, State to State and country to country. It is little wonder they are mostly culled as no-one seems to agree on what to call them, or what they are. I call them Clearwing-modified Dilutes, which is just as confusing, but does indicate that they are different to Dilutes bred from Normals. It may not be the Clearwing gene which alters their appearance but the modifier genes that the Clearwings carry.

Outcrossing To Normals

The significance of single-factor and double-factor Clearwings lies in their interaction with Normals (non-Clearwings). If the Clearwing is double-factor, then when paired to a Normal, all of the progeny will be Normal split for Clearwing:

df Clearwing * Normal = 100% Normal split Clearwing (3)

If, on the other hand, it is single-factor, then half of the progeny will be split for Clearwing and the other half split for Dilute, as follows:

sf Clearwing * Normal = 50% Normal split Clearwing + 50% Normal split Dilute (4)

All of these Normal chicks will be visually similar, and must be further test mated for confirmation as to which carries the Clearwing gene. This is rarely done by those who are brave enough to outcross their Clearwings to Normals. More often they are simply paired back to Clearwings with disappointing results. However, if a Normal split Dilute is inadvertently paired to a single-factor Clearwing, only 1 in 4 of the chicks will be Clearwings. The appearance of a Dilute may also seem baffling, but satisfies the following theoretical expectation:

Normal split Dilute * sf Clearwing
= 25% Normal split Clearwing + 25% Normal split Dilute + 25% sf Clearwing + 25% Dilute (5)

>My own experience with this type of pairing was disappointing, as the Clearwings and Dilutes were too much alike. They did however show some physical features inherited from the Normal outcross. The pairing of a double-factor Clearwing to a Normal split Clearwing was far more productive. It perpetuated Clearwings with good clear wings (not exceptional) and introduced new genetic material into a Clearwing line which must be significantly inbred. I would suggest that the use of a Normal outcross works best when the Clearwing has exceptional wing clarity to begin with. This enables a better chance of excluding the Dilute gene, and also of perpetuating the gene which enables exceptional wing clarity. I am somewhat surprised by breeders who use heavily marked Clearwings when outcrossing to Normals, and then seem to expect the Normal to clean up the wing markings. To me, this has no logic.

The Original Clearwings

At present, there is a growing movement among Clearwing breeders, towards the belief that Clearwings may be split for Greywings which possess full body colour. This has arisen because of the frequent observation that when two Clearwings with exceptionally clear wings are paired together, Clearwings with very pronounced heavy wing markings emerge. These dirty Clearwings are then referred to as Greywings.

Such observations seem to ignore the appearance of the original Clearwings back in the 1930's and 1940's. The first Clearwings did not possess exceptionally clear wings as seen today. Moreover some authors have even suggested that they were developed from Greywings. I do not accept this and believe (as do many others) that they were developed through preferred selection of Clearwings with the clearest wings, generation after generation. This was likely to have been assisted by incorporating an additional modifier gene for exceptional wing clarity. When a dirty Clearwing emerges it has simply lost the additional modifier gene (or possibly genes) and reverted to the original Clearwing form. Some breeders refer to these as single-factor Clearwings, and indeed some may be.

Unfortunately, the fact that some Clearwings with heavy wing markings can qualify as Greywings with full body colour and light wing markings, has added to the confusion. Are they the original Clearwings and not Greywings at all?


The expressions single-factor and double-factor Clearwing, have not gained widespread acceptance in Australia. When they are used, they seem to have a number of totally different meanings. First of these is that double-factor Clearwings have clearer wings than single-factor Clearwings, thus there is a difference in pheno-type. Occasionally, dirty heavily marked Clearwings are referred to as single-factor. The second, is that a single-factor Clearwing is a composite with another variety, for example, as in a Clearwing Spangle. The third is in keeping with overseas usage, and that a single-factor Clearwing is a visual Clearwing but split for Yellow or White (ie Dilute). It follows, that a double-factor Clearwing is a pure breeding Clearwing.<

In adopting the popular overseas usage, I accept that it will be deemed by many as being incorrect (or total rubbish). Nevertheless, single-factor Clearwing is a far easier expression to use than Clearwing split for Yellow or White. Moreover, there appear to no visual differences between a single-factor Clearwing and a double-factor Clearwing, as, for example, among Yellowfaced Blues. There are however, significant differences (in terms of genetic outcome) when they are paired to Normals, or when two single-factor Clearwings are paired together.

While not stated directly, it is also worth appreciating, that if attempting to increase the size of Clearwings, then purchasing large Dilutes from Clearwing breeders may not be such a bad option. It may, in the long term, prove to be more beneficial than using heavily marked, dirty Clearwings, just because they are large.

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