SUTTON 



nance of nvo associated chromarin- 

 entities. 



Dominance is not a conception 

 which grows out of purely cytological 

 consideration. Cytology merely shows 

 us the presence in a cell of two chro- 

 mosomes, either of which is capable of 

 producing some expression of a given 

 character, and it is left to experiment 

 in each case to show what the effect of 

 this combined action will be. The ex- 

 periment ^^ has shown that any one 

 of the three theoretical possibilities 

 may be realized, viz: (1) One or the 

 other may dominate and obscure its 

 homologue. (2) The result may be a 

 compromise in which the effect of 

 each chromosome is to be recognized. 

 (3) The combined action of the two 

 may result in an entirely new cast of 

 character. In cases belonging to the 

 first category, the visible quality (alle- 

 lomorph, chromatin-entity) was de- 

 scribed by Mendel as dominant and 

 the other as recessive, and the experi- 

 ments of Bateson and Saunders and 

 others, as well as those of Mendel, 

 have shown that in many cases a domi- 

 nant character tends to remain domi- 

 nant during successive generations if 

 the environment is not materially 

 changed. Nevertheless, some experi- 

 ments cited by Bateson " go to show 

 that dominance may be variable or 

 defective. Furthermore, it is not only 

 conceivable, but highly probable that 

 in most, if not all cases, there are 

 many different expressions of each 

 character (/. e., many different allelo- 

 morphs as suggested by Bateson in 

 regard to human stature), which on 

 various combinations would neces- 

 sarily exhibit relative dominance. The 

 experiments with peas show an almost 

 constant dominance of certain allelo- 

 morphs, such as round over wrinkled 



^^ Cf. Bateson and Saunders, loc. cit. 

 1" Ibid. 



35 



in seeds, and of yellow over green in 

 cotyledons; but it is worthy of note 

 that here, as in most Mendelian experi- 

 ments, only two antagonistic char- 

 acters have been used. Investigations 

 on varieties, in general similar, but 

 exhibiting different expressions of 

 some particular character, will cer- 

 tainly yield instructive results. Bate- 

 son's observations on crosses between 

 single-, rose- and pea-combed fowls, 

 represent a simple form of such a case 

 and may be expected on completion 

 to add much to our knowledge of the 

 nature of dominance. 



In addition to the many examples 

 brought forward by Bateson in sup- 

 port of the Mendelian principle he 

 cites three types of cases which are to 

 be regarded as non-Mendelian. These 

 are: 



1. The ordinary blended inheritance 

 of continuous variation. 



2. Cases in which the form resulting 

 from the first cross breeds true. 



3. The "false hybrids" of Millardet. 



1. Blejided hiheritajice.—ln treating 

 of this class Bateson clearly states the 

 possibility that the case may be one 

 entirely "apart from those to which 

 Mendel's principles apply," but goes 

 on to show how it may possibly be 

 brought into relation Math true Men- 

 delian cases. He says in part: "It must 

 be recognized that in, for example, the 

 stature of a civilized race of man, a 

 typically continuous character, there 

 must certainly be on any hypothesis 

 more than one pair of possible allelo- 

 morphs. There may be many such 

 pairs, but we have no certainty that 

 the number of such pairs and conse- 

 quently of the different kinds of 

 gametes are altogether iinlhiiited, even 

 in regard to stature. If there were even 

 so few as, say, four or five pairs of 

 possible allelomorphs, the various 



