Revised 22nd of April 2007

Explanation of Gene Symbols used by MUTAVI

By: Inte Onsman, Research coordinator
Research & Advice Group

Uniformity in symbolism on a worldwide basis has not yet been achieved. Will it ever be, that is the question. Since this is the case, we feel the need to explain why we, in some cases, make use of other symbols than in the English language countries.
The system in which the wild-type allele is labelled with a + sign, was already adopted in the early sixties in several continental countries. Therefore MUTAVI, founded in The Netherlands, continued using the system which is very well understood by most fanciers in Europe.
One of the main goals of MUTAVI is the more scientific approach of writing articles in which we cite and refer to scientific literature we studied. In this way we were able to find out how melanocytes produce melanin in mammals and birds and also studied how mutant genes are involved in processes leading to pigmentary disorders in birds.
In some cases we simply prefer to use an abbreviation of the name of the mutation, but in a few cases we prefer to use the abbreviation of the genetical defect or the cause of the disorder. We will now try to clarify some differences between the lists as they were published on the Internet.

The symbol for Australian dominant pied is designated as "T" in the English language countries and designated as "Pb" on the continent. The "T" was probably adopted because it stands for Tyrosinase, the most important enzyme involved in melanin production.
It was believed that the unpigmented areas in pied animals, including birds as well, were caused by the lack of tyrosinase in those areas. Pied animals are very well studied in science and the result of those studies is that nowadays we know that the unpigmented parts of the body in pied animals are caused by the lack of melanocytes in those areas, in fact tyrosinase levels in such animals are quite normal. Even slight amounts of tyrosinase can be found in pied areas because tyrosinase is not totally restricted to melanocytes. Therefore, we chose "Pb" as an abbreviation of Australian dominant pied (Piebald type).

Another major difference is to be found in the multiple allelic series of the dilute (Yellow/White) locus. In the English language countries the basic symbol is "C" and on the continent it was "m". To be honest, the "m" was first chosen because the defect was thought to be the melanin itself, later on we learned the mutation affects the developing of dendrites and therefore obstructs pigment distribution from the melanocytes. After studying cross sections of feather barbs this locus could be identified as the dilute locus and the symbol was changed to "dil".

However, in the MUTAVI listing of genetic symbols the "a" is used to designate the non sex-linked ino which reappeared in the U.S.A. several years ago. The "c" was first adopted by MUTAVI for it is this mutation who represents definitely the gene that encodes for tyrosinase.
Why was originally the letter "c" chosen? There was a reasonable explanation for that.
Melanocytes are specialized dendritic cells in which the biosynthesis of melanin takes place. One of the most obvious features of a melanocyte is that the cell itself is totally transparent and therefore also is called a "clear cell". A melanocyte only becomes visible when melanin synthesis is proceeding and the cell becomes congested with black or brown melanin. An albinotic melanocyte lacks the black or brown melanin and therefore stays a "clear cell" even when it has reached maturity. In science the non sex-linked albino locus is called the c locus and it is probably the most "famous" locus ever investigated. This locus also provides evidence that considerable genic homology exists among the various classes of vertebrates. However, the letter is changed to "a" which stands for "avian autosomal albinism" and is more logical in our hobby.
Nowadays there is evidence that the bronze fallow (FKA German fallow) is allelic with the non sex-linked ino and should be indicated as a bz.

To denote the blue factor we adopted bl because "b" is used for the b-locus in mammals which is the equivalent of the cin-locus in birds. The symbol bw is used to distinguish the recessive brownwing which probably reappeared in Australia. The superscripts designating the multiple allelic series of the bl locus, are abbreviations of the names of the various phenotypes that arose at this locus.

Symbols for sex-linked variaties are simply abbreviations from the name of the trait including the superscript character used for the sex-linked clearbody.

Click here to enter Clive Hesford's homepage for the English language countries listing.

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