62 



PHYSICAL BASIS OF HEREDITY 



and where new ones are being found. For example, if the 

 symbol R (red) is used for the dominant wild eye color, 

 small r would stand for any one of 40 mutant eye colors, 

 and when several of these occur in the same experiment 

 there would be no way of telling for which one the small 

 letter stood. Some other system becomes imperative 

 in such cases, ^ and the most consistent seems to be to 

 use a small letter for the mutant gene in question (or 

 when unknown for the recessive gene), and the corre- 

 sponding capital letter for its allelomorph (usually the 

 wild type). Thus, 5 = short, iS^^tall, 21;:= white, TF = 

 color. The recombination square for the same characters 

 treated above is then: 



Eggs 



Sperm 

 SW 



Sw 



sW 



sw 



SW 



Sw 



sW 



sw 



Since the large letters simply represent the wild type of 

 each particular character it may sometimes simplify the 

 formulae to omit them, or since this may lead to confusion 

 in making up pairs of genes, some convention for wild 

 type, such as N (normal), T (type), or the + sign, or a 

 dash, or a dot may be used. Such short-hand methods 

 are followed by many workers, but it is not necessary to 

 advance the claims of any one of them here. If, for 



* An even more serious objection to the system is explained in "The 

 Mechanism of Mendelian Heredity, " pages 233-235. 



