GENE AND CHROMOSOME MUTATIONS 243 



cially consonants, from the rest of the name, e.g., dw for dwarf, ac for absence 

 of corpus callosum. 



J. Recessive mutations shall be indicated by the use of a small initial 

 letter for the symbol of the mutant gene, the type allele being distinguished 

 by a capital letter, e.g., a for non-agouti, A for agouti. 



4. Dominant mutations shall be indicated by the use of a capital initial 

 letter for the symbol of the mutant gene, the type allele being distinguished 

 by a small initial letter, e.g., Re for rex, re for the type allele of rex. 



5. The icild type may also be represented by a + rather than by a letter 

 when this is more convenient, or by a small letter with a + superscript, e.g., 

 + or /^ for the type allele of T, -\- or a^ for the type allele of a. 



6. Multiple alleles (except lethals) shall be indicated by the use of 

 superscripts (always small letters, never capitals) added to the symbol of 

 the original mutant type, e.g., c^ for extreme dilution. It is suggested that 

 the letter selected be the initial letter of the name of the mutation, e.g., 

 7^^ for the fused allele of brachyury. The initial letter of the name of the 

 discoverer may also be used. Lethal alleles in a multiple series may be 

 indicated by the use of superscript numerals, e.g., f^ and /' for the lethal 

 alleles of brachyury. 



7. Mimics, i.e., mutants of similar phenotype but different location, 

 shall be indicated either by entirely different names and symbols (e.g., In for 

 leaden and d for dilution) or by the same name and symbol with the addition 

 of distinguishing numbers (e.g., wa-i for waved- 1 and wa-2 for waved-2). 

 The latter procedure is not recommended. 



S. In published articles in American journals in which symbols are used, 

 the symbols should be set in italics. 



The Chromosomes of the Mouse 



The mouse has 20 pairs of chromosomes. In males, one pair consists of 

 two chromosomes of unequal size. These are the sex chromosomes, the X 

 and the Y, the X being the larger.* 



Presumably, in course of time, the number of linkage groups in the 

 mouse will come to equal the number of chromosome pairs. At the present 

 time seven linkage groups are known, p c sh-i, d se, hr s, r si, a pa, Ca N and 

 sli-2 u'a-2. In addition to these, nine genes, b, dw,f, hy-i, In, T, v, W and 

 wa-i have been tested against most of the other known genes without 



* Painter, 1928, Genetics 13: 180-189. 



