THE MUTATED GENE 149 



The phenotype of these classes is white, pale yellow, dilute 

 yellow, deep yellow. An assay of the vitamin A content of these 

 four genotypes actually showed its quantity directly proportional 

 to the number of 7-genes, viz.: 



Each F-gene, then, produces about 2.5 units of vitamin. 



Similar examples may also be taken from other endosperm 

 work. Thus, Lindstrom and Gerhardt (1927) found a cumulative 

 effect of the number of starchy genes in maize. As a matter of 

 fact, such relations were already indicated in the first work done 

 on endosperm characters by Correns (1899). A special study 

 was recently made by Rhoades (1936). The case is somewhat 

 complicated in detail. The main feature is that dotted aleurone 

 occurs on corn kernels when a gene Dt is present together with the 

 gene a for colourless aleurone and three more primary genes. 

 The decisive point is that kernels on the same ear may be com- 

 pared which are identical in all the other genes but contain 

 1,2,3 a-genes. The result in regard to the number of spots was a 

 simple linear progression with the number of ai-genes (different 

 numbers of the Dt-gene were, however, not additive). Another 

 example is Nawashin's (1930) work on allotriploid hybrids of 

 Crepis tectorum and C. alpina. The former species has short 

 achenes; the latter, long ones. In the allotriploids, as compared 

 with the parents and F x , a definite seriation of the length of the 

 achenes is found, strictly proportional to the number of alpina 

 (a) and tectorum (t) chromosomes, viz., 



It < 2t + la < t + a < It + 2a < 2a. 



Gowen (1933a) found additive effects similar to those reported 

 in corn when comparing the effects of the Hairy gene in Drosophila 

 in diploids and triploids. Bridges (1922) and Schultz (1935) 

 worked on the fourth chromosome of Drosophila. The latter 

 used the fourth-chromosome character shaven which shortens 

 and removes bristles. He compared the effects in different 

 dosages in diploids and triploids, and the results are proportional 



