Report of the Comittee on Nomenclature

In the TGC report 3:4-5 (1953) this committee published a set of proposed Rules of Nomenclature which it hoped would be adopted by the membership. In the period following the issue of the report it became evident that there were some controversial items in the rules. In particular Item 2, which concerns renaming the linkage groups according to their respective chromosomes, was considered controversial. Also Item 4, which concerns the use of the "+" system as opposed to the commonly used system of capitalizing the dominant expression and using small letters for the recessive expression, was not accepted by all of the membership. Since it is desirable for the rules to represent the desires of the majority of the membership, this committee, on November 10, 1953, distributed a mimeographed discussion of the controversial items to all of the membership. Also included with the mimeo was a post card which would enable each member to vote on the alternative proposals in controversy. The following is a sumarization of this poll;

Gene Nomenclature

  In favor of sp-Sp   scheme      24
  In favor of sp-sp^+ scheme      33
  Undecided                        4
                                  __
                                  61
Numbering of Linkage Groups

  In favor of retaining existing
    linkage group numbers          9
  In favor of numbers based on
    chromosome map                48
  Undecided                        4
                                  __
                                  61

Since the results of this poll have indicated that a majority of the members favor the rules originally proposed by this we now suggest that all of the rules proposed in the 1953 report be accepted as a standard for gene nomenclature.

During the past year several additions and corrections have been made in the list of nomenclatorial rules. We are therefore submitting herewith the revised list.

Rules of Nomenclature

1. Chromosomes. The chromosomes are numbered according to their length as measured in pachetene. Such numbers have already been applied (Barton, 1950), the longest being chromosome 1, the shortest, chronosome 12. In addition to length, such features as position of certromere, amount and distribution of heterochromatin serve to identify each chromosome.

2. Linkage groups. When the work of identifying linkage groups with chromosome is sufficiently far advanced that all groups can bo referred to a definite chromosome, the linkage groups be renumbered so that the linkage groups bear the same numbers as their respective chromosomes. In the meantime it is suggested that linkage groups continue to be designated by Roman numerals and chromosomes by Arabic numbers. For the present, the term "chromosome linkage group" should be reserved for only those cases which have been definitely established. Thus, chromosome 2 and linkage group I are identical (Barton, 1950) and will be designated chromosome linkage group 2 (I) when using the combined term, or simply as linkage group I when the chromosome is not mentioned.

3. Genes. Mutant genes are designated by letter symbols. The mutant name comprises an adjective or noun or a combination of both that refers to the main diagnostic feature of the phenotype. The initial letter of the symbol should be the same as that of the name; additional appropriate letters are added as necessary to distinguish it from other symbols already in use.

After obtaining reasonable evidence for the existence of a new gene for which the phenotyoe can be distinguished reasonably well in some or all genotypic milieux, the discoverer should select an appropriate name and symbol. Symbols that have already been reported should never be knowingly applied to other mutations.

4. Alleles. Dominance or recessiveness of a mutant gene is indicated by comparison with a "standard" or "normal" type. The variety Marglobe is proposed as this normal type since it is widely grown and is typical of the general concept of normal tomato morphology.

A mutant gene which is dominant to the normal type is written with the initial letter of the mutant name and symbol capitalized, while one which is recessive to the normal is written with all letters in small case. The normal allele of a mutant gene is written with the symbol of the mutant gene followed by the superscript "+". Thus the normal allel of sp is sp^+ and of the mutant Wo is Wo^+. A dominant allele appearing later at the sp locus would be designated sp^D. Additional alleles at the same locus are designated by appropriate letter superscripts; thus for the d locus, the following alleles are known: d, d^x, and d^+. Wnen it is clear in the text which gene is concerned, the normal allele may be designated simply by the "+" symbol.

5. Mimics. When new mutants are found which are indistinguishable phenotypically from other previously described mutants, these may be designated by the name or symbol of the original mutant followed by a numerical subscript, the original mutant being assigned the subscript "1", as aready applied in the case of male-sterile mutants, ms\1\, ms\2\, etc.

6. Translocations are designated by the symbol "T". The chromosomes involved in translocations are designated by their respective numbers. In order to distinguish between translocations involving the same chromosomes, small-case letters are used following the chromosome number, thus T(1-2)a, T(1-2)b, etc.

7. Inversions are designated by the symbol "In" while the chromosome in which the inversion occurs is indicated by its respective number. Small-case letters are used to distinguish different inversions on the same chromosome, thus, In(1)a, In(1)b, etc.

8. Deficiencies are designated by the symbol "Df" and are distinguished in the same manner as inversions (rule 7).

9. Primary trisomes are designated according to the extra chromosome present: thus, "triplo-1" refers to the primary trisomic of chromosome 1.

10. In order to distinguish between gene symbols and symbols of the chromosome aberrations, the former are italicized.

11. Since chromosomes of all investigated species of Lycopersicon appear to be almost completely homologous, it is suggested that the same symbolization apply to the entire genus. It is also proposed that the complete gene symbols not be duplicated among the species unless the genes in question are known to be identical, and the key letters of the symbols not be duplicated unless the genes are known to be allelic. Species alleles can be designated by a superscript to indicate the species, for example, a^h for an allele in L. hirsutum.

Committee on Nomenclature

D. Barton, Chairman

L. Butler

J. A. Jenkins