234 APPENDIX 



letter if dominant. With a little practice we have 

 found, from our own experience, there is no real 

 difficulty in making the transition from the presence 

 and absence notation to this one. For example : 



Simplex Duplex 

 Pinkeye 



PvW 



Vermilion eye PvW > w~Tir 



F V W 



PVw 

 White eye PVw ^ PVw 



PVW 



Red eye PVW -* p ^ 



A further simplification would consist in using the 

 letters for the mutant factors alone, as Castle has 

 done, and omitting the normal factors. But in 

 writing out formulae for heterozygous forms, it is 

 often convenient to represent both members of a 

 pair of allelomorphs. In matters relating to link- 

 age it is essential to indicate, in some way, both 

 allelomorphs. 



If in any formula it is desirable to distinguish be- 

 tween dominant and recessive mutant factors, it may 

 be convenient to prime both allelomorphs of a pair 

 in which the factor is named from the dominant 

 character. 



In addition to the more important objections to 

 the presence and absence representation that have 

 been dealt with in the text, there are certain tech- 

 nical drawbacks to the presence and absence scheme 

 of nomenclature that should not pass unnoticed. 



