W. .KlllANNSI'^. — MUTATIONS DANS liKS IJCNRI'S l'UHKS l)K IIAlilCliTS. 



MUTATIONS IN PURE LINES OF BEANS AND DISCUSSION ABOUT MUTATION 



SUMMARY 



In one ol' my [iiirc linos of I)oans, shorplv cliaraelcrized aiiiong ail niy 

 olher liucs, Iwo mulalions hâve occurred. 



The firsl was realizeLl (as a bud-varialion I suppose) in 11)0." and the new 

 biotype was immediately constant. The seeond mutation can Ijotrai'ed back to 

 1!HJ7, and hère the mutant was realize l in i/rlrraz-'/i/nns eondilion. 



The firsl mutant, lioiiiozt/fioii'i iVom the \cry heginning, is characlerized 

 by great size and relative narrow shape of the beans; it may hère be called Ihe 

 narrow blolype. In the second mutation a broad biotype was realized, which 

 could be a e.Ktracted » IVom the original hétérozygote through ségrégation. 

 Owing to the highly transgressive variations it is necessary to know the pro- 

 geny ol' any individual bel'ore it can be recognized as honio — or heterozygous. 

 ^^'e shall not enter the détails of this matter. 



Tlic « Présence and Absence-Theory » seems to be the best base for the 

 further devellopment of hypothèses as lo the nature of ségrégations and muta- 

 tions. But it is necessary to revise the notion «. Dominance ». Dominance says 

 nolhinij as to the positivity of any factor, but it indicates only that afaclor (or an 

 absence of a factor) is ableto realize the character or réaction in question eveii 

 in case of lielerozygosis. And Recessivily means only that homozygosis (as to 

 présence or to absence) is necessary for the realization of the réactions in 

 question. 



The best support for this view is givcn in ail sucii cases, where one single 

 factor (or the absence of one single factor) is the genotypical cause for two or 

 more characlers, some of which are dominant and some récessive. As an 

 example it will suffice to point ont Nilsson-Elile's récent indications about muta- 

 tions in oats. 



Indeed our genelic analysis is moslly purely rclntiri'. Dominance anil 

 Recessivity alone are wholly irrelevant as to the décision of where a positive 

 factor and where an absence is found in the case of ségrégation. And therefore 

 it is highly difficult lo say if a mutation is elTected by an addition or by a loss 

 — by complication or by simplification — of the genotypical constitution of the 

 original liiotype. 



