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?
Summary
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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