34 



thenogenetic egg were the reducing 

 division, the reentrance or suppression 

 of the second polar body would ac- 

 complish the restoration of the oogo- 

 nial chromosome-series. In this case the 

 first parthenogenetic generation might 

 be expected to duplicate the characters 

 of the parent (if environmental condi- 

 tions remained unchanged) and little 

 or no variability would be expected 

 as long as parthenogenesis persisted. 



In relation to these problems there is 

 great need of a simultaneous study of 

 the germ-cell divisions and the varia- 

 tion of periodically parthenogenetic 

 forms. 



We have seen reason, in the fore- 

 going considerations, to believe that 

 there is a definite relation between 

 chromosomes and allelomorphs ^"^ or 

 unit characters but we have not before 

 inquired whether an entire chromo- 

 some or only a part of one is to be 

 regarded as the basis of a single allelo- 

 morph. The answer must unquestion- 

 ably be in favor of the latter possibil- 

 ity, for otherwise the number of 

 distinct characters possessed by an 

 individual could not exceed the num- 

 ber of chromosomes in the germ-prod- 

 ucts; which is undoubtedly contrary 

 to fact. We must, therefore, assume 

 that some chromosomes at least are 

 related to a number of different allelo- 

 morphs. If then, the chromosomes 

 permanently retain their individuality, 

 it follows that all the allelomorphs 

 represented by any one chromosome 

 must be inherited together. On the 

 other hand, it is not necessary to as- 

 sume that all must be apparent in the 

 organism, for here the question of 

 dominance enters and it is not yet 

 known that dominance is a function of 

 an entire chromosome. It is conceiv- 

 able that the chromosome may be 

 divisible into smaller entities (some- 



SUTTON 



what as Weismann assumes), which 

 represent the allelomorphs and may 

 be dominant or recessive independ- 

 ently. In this way the same chro- 

 mosome might at one time represent 

 both dominant and recessive allelo- 

 morphs. 



Such a conception infinitely in- 

 creases the number of possible com- 

 binations of characters as actually seen 

 in the individuals and unfortunately at 

 the same time increases the difficulty 

 of determining what characters are in- 

 herited together, since usually reces- 

 sive chromatin entities (allelomorphs?) 

 constantly associated in the same chro- 

 mosome with usually dominant ones 

 would evade detection for generations 

 and then becoming dominant might 

 appear as reversions in a very confus- 

 ing manner. 



In their experiments on Matthiola, 

 Bateson and Saunders ^^ mention two 

 cases of correlated qualities which may 

 be explained by the association of their 

 physical bases in the same chromo- 

 some. "In certain combinations there 

 was close correlation between (a) 

 green color of seed and hoariness, (b) 

 brown color of seed and grabrousness. 

 In other combinations such correlation 

 was entirely wanting." Such results 

 may be due to the association in the 

 same chromosomes of the physical 

 bases of the two characters. When 

 close correlation was observed, both 

 may be supposed to have dominated 

 their homologues; when correlation 

 was wanting, one may have been 

 dominant and the other recessive. In 

 the next paragraph to that quoted is 

 the statement: "The rule that plants 

 with flowers either purple or claret 

 arose from green seeds was universal." 

 Here may be a case of constant domi- 



^* Bateson's term. 



15 Bateson and Saunders, Experimental 

 Studies in the Physiology of Heredity (Re- 

 ports to the Evolution Committee, I., Lon- 

 don, 1902) p. HI, paragraphs 11 and 12. 



