lot PHYSIOLOGICAL GENETICS 



zygous +/vg- flies at different temperatures. In both cases, 

 the wins area decreases with rising temperature. This they 

 treated as a dominance effed and calculated even dominance 

 coefficients. The assumption, of course, was that vestigial 

 produces a small area. As we know now from Goldschmidt's 

 work, the vg-eSeci has nothing to do with wing growth but with 

 destruction of parts of the wing. A wing without notches is 

 therefore completely dominant. If temperature affects the wing 

 area in either homozygotes or heterozygotes, the ygr-gene is not 

 involved at all but a growth process, primary or secondary (prob- 

 ably only secondary) cell growth. The results therefore have no 

 bearing upon the action of the y^-gene or its normal allelomorph 

 but only upon the problem of whether or not the yo-heterozygote 

 reacts differently from the Wild type in regard to growth under 

 different temperatures. The small difference actually found may 

 have many causes, which might or might not allow conclusions 

 upon genie action. 



The most complete and most thoroughly analyzed data have 

 been presented by Hersh (1930a) for the Bar-eye mutants of 

 Drosophila. Here dominance of the Wild type is not complete 

 (the Drosophila workers call Bar, therefore, a dominant, a rather 

 inexact but useful way of labeling), and therefore a shift of 

 dominance is to be expected. The number of facets in Wild- 

 type eyes and the eyes of the mutant series is a function of tem- 

 perature and may therefore be expressed as a curve for the 

 range of this variable. Hersh (19306) calls such a curve a 

 thcrmophene. If such thermophenes for Wild type, mutant, and 

 heterozygote were compared, they might be parallel. This 

 would indicate that a general process of growth is involved but 

 not the phenomenon of dominance. If a measure for dominance 

 should be introduced, it would remain inconstant through the 

 range of temperatures. If, however, the curve for the hetero- 

 zygote should not parallel that for the homozygotes, conclusions 

 upon dominance might be drawn. In this case, an eventual 

 coefficient for dominance would change over the temperature 

 range. Hersh uses Zeleny's (1920) formula for calculating a 

 coefficient of dominance: 



A A - AA X 

 Co = AT^A^ X 10 ° 



