38 



common function of one of these, 

 there is nothing to show why as a 

 result of some disturbing factor one 

 body of chromatin may not be called 

 into activity in one group of cells and 

 its homologue in another. This would 

 produce just the sort of a mosaic which 

 Bateson and Saunders found in Dattira 

 or as Tchermak's pied yellow and 

 green peas obtained by crossing the 

 Telephone pea with yellow varieties. 

 Correns describes the condition as 

 poecilodyjimnous and his conception of 

 the causes of the phenomenon as I un- 

 derstand it is parallel with that which 

 I have outlined above. The logical 

 possibility suggested by Bateson ^^ that 

 the recessive islands in such cases as 

 the mosaic pea may be due to recessive 

 allelomorphs in the paired state does 

 not accord with the theory of a chro- 

 mosomic basis for those allelomorphs, 

 since the chromosome groups, both of 

 cells showing the recessive character 

 and of neighboring cells showing the 

 dominant one, are derived, so far as we 

 know, by longitudinal or equation 

 division from the chromosomes of the 

 same original cleavage nucleus and 

 hence must be alike. 



The application of the theory here 

 suggested may be put to test by an 

 experiment in which hybrids of dis- 

 similar true-breeding parentage are 

 crossed and a third generation of 

 "quarter-bloods" produced. Mosaics 

 occurring in such an organism, if this 

 theory be correct, would show one 

 character resembling that of one of the 

 maternal grandparents and one resem- 

 bling that of one of the original pure- 

 breds of the paternal side. If both 

 characters of the mosaic should be 

 clearly paternal or maternal the theory 

 as outlined is proven inadequate, since 

 one of each pair of chromosomes, and 

 hence the corresponding character- 



21 Bateson and Saunders, p. 156. 



SUTTON 



group, is thrown out by the reduction- 

 division in each generation. 



In considering the behavior of the 

 two chromosomes forming the basis of 

 any given character, it was noted that 

 in some cases the heterozygote char- 

 acter resulting from the combinations 

 of dissimilar allelomorphs is sometimes 

 totally unlike either of the latter. Thus 

 Mendel found that in crosses between 

 peas respectively 1 and 6 feet in height 

 the offspring ranged from 6 to VA 

 feet. In discussing similar cases, Bate- 

 son calls attention to the light which 

 would be thrown on the phenomenon 

 if we ventured to assume that the 

 bases of the two allelomorphs con- 

 cerned are chemical compounds; and 

 he compares the behavior of the allelo- 

 morphs to the reaction of sodium and 

 chlorine in the formation of salt. The 

 results of chemical analysis show that 

 one of the most characteristic features 

 of chromatin is a large percentage 

 content of highly complex and variable 

 chemical compounds, the nucleo-pro- 

 teids, and therefore if, as assumed in 

 the theory here advanced, the chromo- 

 somes are the bases of definite heredi- 

 tary characters, the suggestion of Bate- 

 son becomes more than a merely in- 

 teresting comparison. 



We have seen reason in the case of 

 the true-breeding hybrids to suspect 

 that the transmission by the hybrid 

 of heterozyo-ote characters may be due 

 to permanent union of the homologous 

 chromosomes. From this it is but a 

 short step to the conclusion that even 

 if, as is normally the case, the chro- 

 mosomes do not fuse permanently, the 

 very fact of their association in the 

 same liquid medium may allow a pos- 

 sibility of a certain degree of chemical 

 interaction. This must normally be 

 slight, since its effects do not appear 

 to be visible in a single generation; but 

 the slightest of variation as a result of 

 repeated new association, even though 



