Symbolisation of genes and alleles

Introduction

In general discussion of primary colour varieties in parrots they, and the mutant genes which produce them, are usually referred to by a name which is appropriate to the effect which is produced in the species being considered. That may vary depending upon the original colour makeup of a species. A number of varieties and the responsible genes occur commonly in a many species. It is usual to capitalise the name (for example: Blue) when referring to the bird itself and to use lower-case (blue) when referring to the gene which produces that variety of bird.

Quite frequently the effect produced by a gene, and therefore the suitability of a name, depends upon the presence or absence of other genes. Most often, and most noticeably, this happens with what are generally referred to as green-series and blue-series birds. In such instances we can end up with as many as four names: one for the green-series variety (e.g. Lutino), one for the blue-series variety (e.g. Albino), one for the parblue variety (e.g. Creamino) and, finally, a fourth for the gene itself (e.g. ino).

An example of the varying colour effects produced in differrent species is the blue locus, where alternative forms of the same gene which produce Parblues and Blues in most species, instead produce the Paleface and Whiteface in the Cockatiel. It is readily apparent from these examples that the basic function of alleles at this locus is the control of yellow pigment production.

The symbols

In more specific genetic discussion, where pairings may be represented by formulae, it is convenient to use symbols to represent these mutant genes, or alleles, and their wild-type counterparts. The time honoured system, similar to that first used by Gregor Mendel himself, is to represent the gene pairs by the initial letter of the colour variety which the mutant allele produces: for example, in the case of the Blues, upper-case (B) for the dominant allele (the wild-type in this instance) and lower-case (b) for the recessive allele.

Where a gene has mutated more than once to produce a number of alternative alleles, those which lie between the wild-type and the most recessive form are identified by adding a suitable superscript character. (There are detailed discussions on this subject at Inheritances patterns - multiple alleles and The Parblue puzzle in these pages.)

Each individual gene or one of its alleles has its own unique position on one of the chromosomes. The locus also takes on a name which may be that of the first mutant form to be identified as due to an mutant allele at that locus or, more usually, the most recessive mutant form found at that locus (e.g. the blue locus).

Europeans are more professional

A variation of the above system, in which the wild-type allele is labelled with a ⁺ sign, is used by many professional geneticists. This system has never been widely adopted in aviculture and I have avoided it as an unnecessary complication and distraction. For the same reasons, there would be no gain from adopting the more technically correct ZW notation for the sex-chromosomes as some purists might argue.

However, it has been drawn to my attention by Inte Onsman of Mutavi that the system mentioned above is in widespread use in Holland, and therefore probably much of Northern Europe, and that this is the symbolisation which will be used in the Mutavi pages. In these circumstances it seems appropriate to briefly consider the modifications which have been made to the system we are already familiar with.

As in the original system an alphabetical character is assigned, and chosen in the same manner, as a base symbol to represent the two or more alleles at a particular locus. This time, however, the symbol is in the same case for every allele at that locus. If the mutant allele is dominant all are represented by an upper-case character; and if the mutant allele is recessive all are represented by a lower-case character.

To differentiate and identify the wild-type allele the base symbol is labelled with a plus sign in superscript. So the blue alleles mentioned above would be b⁺ (wild-type) and b (mutant type). As before, any intermediate alleles in a (multiple-allelic) series have their own unique superscript character. To add to the initial confusion, it has become normal practice to omit the base symbol for the wild-type allele leaving it identified only with the superscript ⁺ sign.

Plethora of names

Naturally, as the number of varieties continues to increase, both within individual species as well as across the broad range of parrot species, duplication of initial letters becomes a problem. In such cases a second initial within the varietal name (or even the initial of a syllable) may suggest itself, or two letters may be used when all else fails. In any event the various organisational bodies within aviculture, together with prominent writers on the subject, should make every effort to adopt and use terminology which is as standardised as possible.

Allied to this issue, and probably of even greater significance, is the standardisation of the varietal names themselves. It becomes very apparent how difficult it is to achieve uniformity on a worldwide basis when, even within individual countries, we see disagreements over nomenclature. For the present, in the case of many varieties, it will have to suffice to establish where different names are synonymous and refer to the same variety. Adding to the these problems is the fact that birds of quite differrent genetic constitution may appear virtually identical visually.

The Budgerigar

In Genetics for Budgerigar Breeders, Taylor and Warner published a table of proposed names and symbols for the budgerigar primary varieties then in existence and the genes responsible for these varieties. By and large these names and symbols have been honoured by informed writers even, where appropriate, when discussing species other than the budgerigar. Over the intervening years however, a number of varieties have disappeared, other varieties have been established, a few names have tended to be truncated, and the genetics of some varieties has been clarified.

Below, I produce a new listing in which these changes have been taken into account. The varieties are grouped by their mode of inheritance which enables multiple allelic series to be appreciated in their proper context. In such cases varieties are listed downwards in order of dominance, although you should be aware that codominance can exist between alleles in a series (e.g. greywing and clearwing). I make use of the term incomplete-dominance in those cases where codominance involves the wildtype allele since this is the way most breeders view these varieties.

In general, I have retained the symbols initiated by Taylor and Warner and where it seems sensible retain use of only one character for the sake of simplicity. However I bear in mind the listing given at Mutavi, where Inte Onsman seeks to tie in the symbols used with those established in scientific literature, and the emergence of a number of new varieties which I recommend that you also visit.

LIST OF BUDGERIGAR VARIETIES AND SYMBOLS

Notes:

1. There are technical reasons to believe that the german fallow and NSL ino might be alternative alleles at the NSL ino locus. However, I am not aware of definite breeding proof that this is so and list them separately until there is conclusive evidence one way or the other. Although the NSL ino appears to maintain a fleeting and elusive presence within (Danish) Recessive Pied stocks in the North West of the country (UK), obtaining specimens to test this theory will be difficult. [The Scottish Fallow is omitted since there are now no identifiable strains of this variety being bred.]
   
   
2. Brownwings are being bred in Australia, but it is not known whether this is identical to the Brownwing formerley present in the UK. There have been indications that Brownwings are again being cultivated in the UK and I would be pleased to hear from anyone who can confirm this.
   
   
3. A Recessive Grey form is being bred in small numbers in Australia but is not as dark as the now lost English Recessive Grey and feather analysis has shown it to be different.
   
   
4. There is good reason to believe that the Dutch Dominant Pied and the Continental Clearflight have a close relationship, since both combine with the Danish Recessive Pied to produce the Dark-eyed Clear and both appear to throw the odd 'Frosted' form. However although Clearflights continue to be bred in the UK, mainly in order to produce Dark-eyed Clears, no Dutch Pied types seem to appear. It may be that the two have an allelic relationship or perhaps a closely linked modifying gene is present in one form. Although I have assigned the same gene symbol to both, they are listed separately until such time as their relationship is fully clarified.
   
   
5. The Greywing, Clearwing, and Dilute, are caused by a series of alleles all recessive to the wildtype. Within this series the greywing and clearwing alleles are co-dominant and the dilute is the most recessive.

Further comments:

The Australian Dominant Pied is now commonly referred to simply as the Dominant Pied and most of those seen on the showbenches are very sorry examples of the variety. (I believe some Australians even go so far as to call them English Dominant Pieds — good on yer!) Similarly, the Continental Clearflight has lost the reference to its origins and now comes in a plain brown wrapper marked Clearflight. This short-sighted attitude, instigated by the Budgerigar Society, may cause difficulties should similar varieties occur or be re-introduced. The original names were chosen with this possibility in mind by wiser predecessors.

The Slate has made a welcome return to the UK thanks to Inte Onsman, of Holland, who let Cyril Rogers (now sadly deceased) have a few examples of the variety. These are now being worked with by members of the Rare Variety and Colour BS and appear to have an assured future.

New varieties added are the Texas Clearbody, now well established in the UK, and the Saddleback which is an even newer import. (See the external articles The Clearbody, by Kevin Eatwell, and Saddlebacks — a New Mutation in the UK (UGH!), by Ghalib al Nasser; both at Budgerigars Galore. Also included are the Faded, the Blackface, and the Mottle, which so far as I know have not yet been introduced to the UK. I am unaware of the fate of the Easley Clearbody.

You may be surprised to see the Violet listed as a incomplete-dominant variety. However this was well documented by Taylor and Warner and has been further investigated by Peter Bergman of Australia. His article on the subject, The Facts About Violet Budgerigars is in these pages.

The genetics of the Yellowfaces and Goldenfaces has been clarified since the publication of Genetics for Budgerigar Breeders; initially by Ken Gray in a series of published articles, and even more recently by Peter Bergman who first introduced the concept of two genetically distinct Blue budgerigars in his article Gene Function in Yellowface Budgerigars in these pages. The Yellowfaces and Goldenfaces are classed as Parblues which occur in a number of species. You can read an assessment of present thinking on this subjecy in my series of articles The Parblue Puzzle which includes links to other external articl

Please be aware that I have deliberately omitted the capital X (representing the X-chromosome) from the symbols for the sexlinked varieties; this is quite normal practice since it tidies up the formulae used to represent different pairings, and the X can be inferred from the presence of the Y which is always included. (Besides, most browsers don't handle superscript characters gracefully and I hate to think what they would do with double superscript notation — may I commend MSIE 4 (and now v.5) to you as a notable exception to this generality.)

Composite varieties

A composite variety is one in which the effects of two or more distinct colour genes are expressed. However a little common sense has to be exercised in this regard since a variety such as the Cobalt budgerigar, with its blue and dark genes, is technically a composite. In fact any blue series apart from the Skyblue falls into this category.

Composite varieties are sometimes referred to as compound or secondary varieties. The first of these alternatives is acceptable since it conveys a similar though not identical meaning. The second (secondary !) has a meaning with no relevance to the coming together of two or more visual effects and its use is to be discouraged.

Other Parrots

A number of the primary varieties which occur in the budgerigar, and the responsible genes, also now occur quite commonly in other parrot species. Indeed the number of varieties in the Indian Ringneck now probably exceeds that in the budgerigar by some margin. The following fall into this category and there seems little reason in most instances why they should not use the same symbols.

Copyright: Clive Hesford, March 1998 (latest revision August, 2001)

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