Vererbung, Variation, Mutation. 79 



priuiären Mutationen (gelb und schwarz) und stellen eine „Permutation" dar. Der 

 braunen Form fehlt sowohl der Faktor für schwarz als auch derjenige für gelb 

 (braun = byBr). Sämtliche Mutanten erscheinen weniger kräftig als die Wild- 

 form. Am stärksten wird die braune Permutation von dieser Schwächung be- 

 troffen, am wenigsten die schwarze Mutation. 



Der Faktor für schwarz ist geschlechtsbegrenzt: nur die 5 bestimmenden 

 Spermatozoen führen B mit sich, 



Parallele Erscheinungen — Vorhandensein von mindestens drei Faktoren 

 zwecks Entstehung der normalen Farbe und geschlechtsbegrenztes Verhalten 

 wenigstens eines derselben ■ — ließen sich bezüglich der Augenfarbe von J)roso- 

 plüla feststellen. Irgendwelche Korrelationen zwischen diesen beiden Faktoren- 

 reihen scheinen jedoch nicht zu bestehen. M. Daiber (Zürichj. 



213) Morg'aii, T. H. (Columbia University), Factors and unit-characters 

 in Mendelian theory. In: Amer. Natural, Bd. 47, Heft 1, S. 15—16, 1913. 



In this paper the Mendelian hypotheses of factors and unit-characters are 

 considered, both as regards the underlying conceptions and the symbolism by 

 which they are to be represented. Morgan points out that a unit-character 

 can not be the product of a particular factor acting alone, but the whole orga- 

 nism is in some way concerned in its production. 



In his experiments \\\i\\ Drosophüa, Morgan has obtained from a pure wing- 

 less race one iudividual having one normal wing. The condition was not inhe- 

 rited, but such cases lead to the belief that the appearance of a new recessive 

 character is not due to an irretrievable loss from the germ plasm, but rather to 

 a readjustment of the equilibrium. 



Regarding the symbolism for Mendelian characters, the author points out 

 that when a Single character-difference exists for a given organ the nomencla- 

 ture of Mendel himself may be conveniently used. Thus in Drosophila, R = red 

 eye and V = vermilion eye. But this method breaks down when two new cha- 

 racters of the same organ are involved. The presence and absence hypothesis 

 was invented to cover such cases. In BrosophUa the appearance of a pink-eyed 

 mutant necessitated the use of this hypothesis as follows: red eye = RV, ver- 

 milion = rV, pink = Rv. Thus vermilion X pink = rVRv (red) F^, and in Fg 

 a new type, rv (orange eye), appears, for which the symbol was adopted. The 

 difficulties with this scheme are, (1) that it implies the actual loss of two "fac- 

 tors" from the original germ plasm, PVO, and (2) that the whole System of 

 Symbols must be changed when a new mutation ("eosin") in eye color occurred. 

 The method suggested is as follows: The first letter of the new character shall 

 stand as its symbol. Thus P Stands for the pink "factor", and p for the corre- 

 sponding factor of the pink-eyed fly. The formula for red eye will then be PVE, 

 for vermilion, PvE, etc., new capital letters being added to the formula for red 

 eye a\ heuever a new recessive mutation occurs, and a new small letter whenever 

 a dominant mutation occurs (the character itself being represented by a capital 

 in the latter case). The same symbolism is applied to three mutations for body 

 colour and eight mutations in the wings. Thus P represents the pink "factor", 

 i. e., the thing which has disappeared in the redistribution accompanying the 

 change from red to pink-eye, while p represents the corresponding factor of the 

 pink-eyed fly. 



The writer points out that, as ordinarily used, a double meaning is attached 

 to the Symbol for a given factor. Thus P in the formula vP meant a residuum 



