54 GENETICS 



another germ-cell (See Chap. X). In this instance 

 its effect may be profound and patent upon the entire 

 development of the individual, although if it chances 

 to be relegated to an abortive polar cell during meiosis 

 or to an unmated spermatozoon it will be entirely lost 

 at once. There are no doubt many such "mute inglo- 

 rious mutations" (Muller) that never see the light 

 of day. 



It is furthermore obvious that a gametic mutation 

 usually enters the organism concerned singly, that is, 

 from one parent only, and if recessive 'in character 

 will fail to put its appearance in the somatoplasm 

 until some subsequent generation when two hybrids 

 from the new stock each chance to contribute the re- 

 cessive mutant character in question to the formation 

 of a new individual. 



The appearance of such mutants, therefore, unless 

 dominant, must come two or more generations after 

 the mutation has taken place. The time when a 

 gametic mutation is initiated, consequently, and when 

 it manifests itself are by no means necessarily the same. 

 This fact needs to be kept in mind in considering the 

 evidences from experiments for the determining causes 

 of mutations. 



Perhaps the reason why mutations are more fre- 

 quently reported in self-fertilizing (autogamous) 

 plants than in cross-fertilizing (heterogamous) ani- 

 mals is because in self-fertilizing organisms the inbreed- 

 ing necessary to bring about the doubling of a single 

 character so that it will come into expression is more 

 likely to occur. 



