344 



in millions. 11, serins almost impossible in believe thai we should liave ever 

 found sncli a mutant. 



5. The experimental evidence shows there are many factors arranged 

 in a linear series on the X chromosome. Some affect wings, some body 

 colors, others the shape of the eye, and so forth. Sturtevant has pointed out 

 the significance of the fact in light of the above statement that the characters 

 which behave as members of a multiple allelomorph system arc closi I 

 related physiologically. 



G. If the mutants are the result of changes as shown in Kig. D it would 

 seem as if a mutated stock would more readily give rise to subsequent mu- 

 tations, since fewer simultaneous losses are necessary. As a matter of fact 

 four of the members mutated directly from red while eosm came from white. 



7. Morgan has emphasized the idea that it is difficult to accounl for 

 reverse mutations on the assumption of losses from a completely linked chain 

 of loci, as the Presence and Absence theory postulates. On the other hand 

 it is conceivable how such a reaction could come about if the mutant is the 

 result of an expression of something analogous to an isometric change. 



8. Is chromatin such simple material that the only change conceivable 

 is a loss? 



Literature Cited. 



1. Morgan, Sturtevant, Muller and Bridges. Mechanism of Mendelian 

 Heredity. Henry Holt. 1915. 



2. Bateson, William. The Address of the President of the British Asso- 

 ciation for the Advancement of Science. Science. August 28, 1914. 



3. Hyde, Roscoe R. The new members of a Sex-Linked Multiple 

 (Sextuple) Allelomorph System. Genetics. November 1916. Princeton 

 Press. 



