SHORTER ARTICLES AND DISCUSSION 



PIEBALD RATS AND SELECTION, A CORRECTION 



In a recent important publication Dr. Sturtevant makes "an 

 analysis of the effects of selection" in which he ably maintains 

 the current view that the single gene is not changed by processes 

 of systematic selection. His argument rests on a careful experi- 

 mental study of the behavior of the character "dichaet" in Bro- 

 sophila, followed by a general discussion of other work, my own 

 in particular. I am represented as completely opposed to his 

 view, and so I have been at times, but such is not the case at 

 present. I agree so fully with his general conclusion that I want 

 to obviate needless discussion based on the misapprehension. 



I thought two years ago that I had evidence that a single gene 

 had changed in the course of a selection experiment, this gene 

 being concerned in producing the hooded pattern of rats. I now 

 find this view rendered untenable by further experiments, the 

 results of which are in course of publication. These results 

 show that the supposed changes in a single gene are more prob- 

 ably due to changed residufil liercdity, wliicli very likely may 



The crucial experiment cip mi-..., s^I \,^ \)v Sewall 



Wright. The divergent lumdr,! v.u-.-^. ••phis .m.l ••minus." re- 

 sulting from selection, were to be ci'ossed reitcatedly with a third 

 race, the hooded character being recovered as a recessive in F., 

 following each cross and its variability compared with that of 

 the uncrossed race. It was believed that if multiple modifying 

 genes were involved, repeated crossing with a pure third race 

 would tend to remove these, in which case the extracted hooded 

 character being deprived of its plus modifiers would be sub- 

 stantially identical with the hooded character deprived of its 

 minus modifiers, as seen respectively in hooded recessives derived 

 from the plus and from the minus crosses. Well, they are sub- 

 stantially identical, but it has taken some time imd a good deal 



