No.658] SHORTER ARTICLES AND D1SCU88I0H 373 



aBcdE 

 AbCDe 



In all problems relating to crossing-over of the factors from the 

 one series to the other the location of each factor (and its allelo- 

 morph) is expressed by the formula just given, whereas one in 

 which even the duplex condition is represented by small letters 

 in a single line (abcde) fails to indicate the order of the factors 

 in their mutual relations in the two series. 



3. In cases in which sex-linked factors are involved the half 

 formula of the female will sometimes suffice (if thought of in 

 duplex), but in the male the half formula will not suffice when 

 some of the factors are sex-linked and others not. If a and b are 

 sex-linked, then the formula abcde fails to represent the condi- 

 tion in the male, for only cde are present in duplex. 



In contrasting his scheme with mine Castle (page 176) uses the 

 full formula? for my cases and the abbreviated formula? for his 

 own, to the apparent advantage of the latter. If he tried to 

 express in his formula? what I have expressed in mine, and had 

 omitted from my formula? what he omits from his own, the ad- 

 vantage would have appeared differently. For shorthand pur- 

 poses the most abbreviated form of any system will be employed 

 in each particular case, except where for special reasons the 

 '•"inparative formula, in spite of its length, gives a clearer idea 

 of the relations involved. When representing eye colors, for 

 instance, we put into the formula? only the symbols for the 

 particular eye colors under consideration, but not, of course, 

 tlif symbols for other eye colors that are not being used. Castle 

 gives the impression that I would use all the known symbols for 

 eye color each time I wrote out the formula for the eyes, but 

 obviously nothing of the sort is intended, for we have other eye 

 colors that do not appear in papers that are not concerned 

 with them. 



Castle uses small letters for the recessive mutants, as I also 

 propose to do in exactly the same sense. He scores a point— 

 admittedly— when he says that in my formula? the factor B which 

 he reads as black is the only factor that is not present in the 

 black fly. There is just one unfortunate line on page 13 that 

 gives Castle the opportunity to make this jibe, while the whole 

 spirit of the paper goes to show that the small letter stands for 

 the factor carried by the recessive mutant. In order that no 

 misunderstanding of this sort may again arise let me state that 

 small p is the factor for pink; small 6 the factor for black; 

 small v the factor for vermilion ; small m the factor for minia- 

 ture. The allelomorphs of these factors in the normal flies are 

 dominant and are represented by the capital letters P, B, V, M. 



