GENERAL CONCLUSIONS 303 



ported by Hance in Oenothera and in several other cases. 

 The temporary separation and reunion of certain chro- 

 mosomes in moths, described by Seiler, also come under 

 this heading, especially if, as he supposes, the separated 

 elements may sometimes recombine reciprocally. 



In contrast with the effect produced when large num- 

 bers of genes are involved, the effects produced by a 

 change in a gene appear at first sight much more ex- 

 treme. This first impression may, however, be very mis- 

 leading. While it is true that many of the most striking 

 mutant characters studied by geneticists are markedly 

 different from the normal character with which they are 

 contrasted, these mutant characters have often been 

 chosen for study because they are sharply marked off 

 from the typical character, and can, in consequence, be 

 readily followed in succeeding generations. Their sepa- 

 ration is accurate, and the results more certain than in 

 cases where the differences are less marked, or where 

 there is an overlap between the characters of the con- 

 trasted pair. Moreover, the more bizarre and extreme 

 modifications, that sometimes amount to "abnormali- 

 ties," are the ones that are most likely to attract atten- 

 tion and interest, hence are utilized for genetic study, 

 while the less obvious modifications are overlooked or 

 neglected. Geneticists are familiar with the fact that the 

 more intensively any particular group is studied the 

 more mutant characters are found which had been, at 

 first, overlooked, and since these are those that more 

 nearly approach the normal type, it becomes increasingly 

 evident that the mutation process involves very small, as 

 well as very great, modifications. 



In the older literature the extreme, abnormal types 

 were called sports, and for a long time it was supposed 

 that these sports were sharply separated from the small 

 or individual differences constantly present in all species 



