APPENDIX 2 



subscript or superscript. The same practice may be adopted for homologous 

 chromosomes from different strains of a species. 



In Drosophila genetics the special symbols In and Tr are used to indicate 

 inversions and interchanges. The chromosome or chromosomes involved and the 

 special name of the structural change in question are appended, e.g. In{i)(il-4g, 

 is the delta-49 inversion in the X (or ist) chromosome. Special composite 

 chromosomes may also receive special names and symbols as in the case of the 

 6 compound X chromosome. 



The German investigators of Antirrhinum and other organisms have adopted 

 a system whereby each gene is given a three-letter symbol. In the case of a multiple 

 allelomorph the superscript also has three letters. Thus the peloric gene is pel and 

 the tincta allelomorph in the pallida series is pal"". While achieving uniformity 

 of symbolism this system is apt to defeat its own ends since it is easier to write, 

 for example, tincta than pal"". 



For Lathyrus, Punnett proposed a symboHsm based on linkage relations. Each 

 chromosome was given a letter, each gene taking the letter of its chromosome 

 and a subscript number indicating its place in the order of genes known to be 

 borne on that chromosome. The difficulties arising from insufficient knowledge 

 of linkage relations and the placing of new genes inside an estabhshed linkage 

 group require no stressing. The system has achieved httle popularity. 



In human genetics the symbolism is so varied as to verge on the chaotic. Many 

 character differences are known to be hereditary without, however, the exact 

 mode of inheritance being clear. No symbolism is then possible. Even where 

 the mode of inheritance is clear it is often portrayed in the form of pedigree 

 diagrams with empty, hatched or filled circles or squares to denote the phenotypes 

 and assumed genotypes. Sometimes symbols according with one or other of the 

 regular systems are allotted; but often, even where symbols are used, the usage 

 bears no relation to any wider scheme. Thus with the blood groups the three 

 main allelomorphs are A, B and O, and when two A type allelomorphs are 

 distinguished it is by subscripts as Aj and A2, not by superscripts. With the 

 Rhesus blood group allelomorphs the haphazard symbolisms which had grown 

 up independently in Great Britain and the United States are now being superseded 

 by a more rational system due to Fisher, which takes into account the antigens 

 and antisera concerned. Increasing genetic research in man must in time demand 

 a similar rationaUzation of symbohsm for other genes whose differences are 

 commonly observed. 



Various moves have been made towards a codification of genetical symbohsm, 

 the question having been discussed especially by de Haan (1932, Genetica, 15: 

 1-21, 219-223). No universal system has, however, been developed and adopted 

 as such; though, as will have been seen, the two most widely used systems have 

 very much in common. 



3. Statistical 



The various letters, Greek and Latin, are frequently used to suit the convenience 

 of the moment in statistical accoimts. Certain conventions are nevertheless widely 



431 



