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I'UYSlOUxncM. CENETICS 



to the quantity considering the diploidy or triploidy of the other 

 chromosomes, as Table 15 shows: 



Table is 



(From Schultz) 



2A 



SN 



Haplo IV 



Ebctreme sv 

 Dies 



Diplo IV 



sv/ + 



Triplo IV 



sv/sv/sv 



Type sv 

 Ebctreme sv 



+ 

 Slighl sti 



Tetra IV 



sv/ sv/sv/sv 



Extra bristles 

 Slighl so 



Dosage differences of this type will be found in many cases of 

 polyploidy and hyperploidy, and examples may be cited from 

 innumerable cases in plants, in which individual genes are com- 

 pared in different dosages within these systems and produce 

 quantitatively increasing effects. Some important facts derived 

 from the study of tetraploids by Lawrence and Scott-Moncrieff 

 will be reported in a later chapter. 



At this juncture, it ought to be pointed out that in all cases 

 where multiple factors show a simple additive behavior a simple 

 quantitative relation may be involved. If we take, for example, 

 Nilsson-Ehles' classic case of the color of oats, the quantitative 

 effect of one to six multiple genes may be based upon each 

 gene's contributing something to the amount of oxidase produced 

 (or chromogen or time of onset, etc.). In most cases, a further 

 analysis is not possible. Where, however, the individual genes 

 have been isolated, as in the nun-moth case, (see page 128) and 

 their individual action is known, conclusions upon the action of 

 different quantities of similar genes may be drawn. There are, 

 of course, many pitfalls to be reckoned with. To mention only 

 one: Rasmusson (1933) finds that multiple genes do not act in an 

 additive way but more in the form of an interaction with a 

 combined effect lower than required if additive. Such a result 

 may mean very different things in terms of gene action, such as a 

 threshold or saturation effect, as in the bobbed case of Stern; a 

 mutual dependency of different reactions leading to the same 

 end product; saturation effects only within individual members 

 of the series; disturbance of time relations; disturbance of 

 reactions by others. In any case, conclusions must be carefully 

 weighed. 



