154 



PHYSIOLOGICAL GENETICS 



therefore, that in the hybrid these two genes work against 

 each other and thus control the asymptotic increase in cell 

 volume. A- the curve of the combined effect is the curve of a 

 monomolecular reaction, he concludes that the action of the 

 genes in this case is of tins general type and follows the mass law 



/*- — 



Uni Bi Tri Quadrl Octo Sedecivalens n— *• 



Fig. 31. — Curves for cell volume in polyploid mosses (n to 16n chromosomes) 



.... and pure species, — -- hybrids with regulation. (From Wettstein, 



1924, Biol. Zentralbl. 44.) 



of reaction. This conclusion then coincides with those derived 

 from many other facts. 



E. The Heterozygote as Dosage Difference 



In a former chapter, the facts relating to the gene in hetero- 

 zygous condition wen' analyzed. We mentioned there the 

 presence-absence theory and also the possibility that a pair of 

 genes differ quantitatively. In cases of multiple alleles, it could 

 be said at least that the activity or potency of a pair of alleles 

 was different in quantity, whether this meant quantity of the 

 genes themselves or not. It was then found that in cases of 

 actual quantities, as in the Bar case, the heterozygotes fitted 

 into the seriation. All this suggests that mutant differences are 



