THE MUTATED GENE 207 



There are several cases involving this so-called maternal 

 inheritance, in which it is difficult to form an idea of the type of 

 prefertilization influence of genes upon cytoplasmic structure. 

 In some of these cases, it is not even completely certain whether 

 or not the interpretation is correct. Thus, Morgan (1912, 

 1915) claimed a prematuration effect to explain irregularities in 

 the inheritance of the gene rudimentary; Lynch (1919) applied 

 the idea to an explanation of sterility in rudimentary and fused 

 (Drosophila); Redfield (1926) claimed maternal inheritance for 

 a sex-linked lethal in Drosophila which acts only when the mother 

 is homozygous for a second chromosome gene; Gabritschevsky 

 and Bridges (1928) found a maternal effect upon the eggs of 

 homozygous females for an enhancer gene of giant in Drosophila. 



Rather remarkable are such cases of maternal inheritance in 

 which the effect of genes acting upon the organization of the egg 

 cytoplasm prior to fertilization becomes visible only in later 

 developing parts of the body. Dobzhansky (1935) found such 

 an effect in reciprocal crosses of two races of Drosophila pseudo- 

 obscura, controlling the size of testes. An autosomal gene acting 

 on the egg plasm is responsible. In this same form, Dobzhansky 

 and Sturtevant (1935) described a number of further hereditary 

 characters with maternal inheritance, viz., viability, sex ratio, 

 rate of development. The latter characters may be understood 

 more easily as controlled by a general plasmatic condition induced 

 by genes. There is also a statement by Warren (1924) that egg 

 size in Drosophila is controlled thus. It is more difficult, how- 

 ever, to understand the findings of Timofeeff (1935) that a gene 

 controlling the pattern of bristles in the thorax of D. funebris 

 (polychaeta gene) shows maternal inheritance. A predetermina- 

 tion of a pattern of thoracical epidermis in the cytoplasm of the 

 egg is more than could be expected even in cases of develop- 

 ment with very early determination (self-differentiation). 



There are many facts showing that details of later stages of 

 development are influenced by mutant genes. The whole body 

 of work upon Mendelizing characters of larvae of insects (silk- 

 worm, Lym,antria dispar, and L. monacha by Toyama, Tanaka, 

 Goldschmidt, etc.) could be mentioned. There are also larval 

 characters in Drosophila controlled by genes (Chubby, Dobzhan- 

 sky and Duncan, 1933). In plants, all the endosperm and coty- 

 ledon characters belong in this category, also characters of the 

 protonema in mosses; moreover, the influence of genes upon rate 



