MENDELIAN FACTOE DIFFERENCES VEESUS 

 EEACTION SYSTEM CONTEASTS IN 

 PIEEEDITYi 



T. H. GOODSPEED AND R. E. CLAUSEN 



During recent years there lias been a remarkable ad- 

 vance in our knowledge of Mendelian principles of hered- 

 ity. This advance has for the most part had its source in 

 the important and fundamental work of Morgan and his 

 associates (1915) in which they ha^e been concerned with 

 the mutations of the common fruit fly, Drosophila ampe- 

 lophila. The results of other work, in so far as agreement 

 has permitted, have been brought into harmony with the 

 principles arrived at through these investigations. As a 

 result there has been developed a ffarly clear and compre- 

 hensive conception of the constitution of the hereditary 

 material and the natiir(^ of the Tnochanism by wliidi it is 

 distributed in gamoto.izciH'-i-. ;i cniici']!! ioii wliidi fur- 

 nishes a consistent exi.ilanatioii of tlir ]»n)(]urts of Men- 

 delian studies. 



Morgan has stattMl tliat tlic fuiidaiuental principle of 

 Mendelism may he I'l'ilnccd to this, that the units con- 

 tributed by two i.ar('Tit< x'parato in the germ cells of the 

 offspring without liaxin-- liad aiiv effect on each other. 

 This conce]>tioii of tlic abx'iK'c of any factorial variability 

 save that coiiccnitMl in tlic di^'ontiiiuous changes in fac- 

 tors involvt'd ill inutations lias fni-nislied the working hy- 

 pothesis for ^loi-airs brilliant nrialy>i> of the germ 

 pla-Jii ..f PrnsniJuhi. Altliou.u-h tlu' n'sults of the Droso- 

 pliihi invotiuatioiis havi' Itocn ably pi-e-(>?ited elsewhere 

 (Morgan ot ah. /. c) it s('(>tn< well brirlly to review them 

 hero es]»(M-ialh- as thcv arc \ ital to the arunniont presented 

 in this pap<'r." 



