GENES MODIFYING NOTCH. 



371 



in the egg. But since bent flies with the character well developed may 

 not produce, when bred to each other, any more flies of their own kind 

 than do their normal appearing brothers and sisters, there is nothing 

 gained by making such an assumption. On the contrary, it seems 

 more reasonable, I think, to suppose that the same environment (in 

 the widest sense) that is favorable to the full development of the bent 

 characters make that character the more effective in its influence on 

 short Notch. It seems to me hazardous to base any view concerning 

 the nature of the gene itself on evidence of this kind, as has been done 

 by several recent writers. 



FIG. 95. 



CROSSES BETWEEN SHORT NOTCH AND OTHER STOCKS. 



Unless the modifying factor for short-Notch is partially dominant or 

 unless other stocks carry the modifier, or some other dominant modi- 

 fier, the expectation on crossing short-Notch females to males of other 

 stocks is atavistic types of Notch females. The males of short-Notch 

 stock carry in their sex chromosome, as has been shown, a modifier for 

 short-Notch; hence crossing of such males to selected or to atavistic 

 Notch are expected to show some influence on the character of Notch 

 in their daughters if the factor is dominant or partly so. In the light 

 of these expectations the following crosses are not without interest. 



