Chromatin as ''Hercd'itarif Substance'' JJ5i) 



each chromosome of any series, lias a corresj)()ii(lin«r one in any 

 other series, and if these have such an identity and fr<M(l.)m 

 to combine and separate as the discussion had assunicd, tli.n 

 if a given chromosome of the father be desip:nated by ./ .-md its 

 mate in the mother by a, in synai)sis there wouhl arise Aa, wiiieh 

 on reduction division preparatory to ripenin<>; of the eg^s and 

 sperm would produce two kinds of eggs and two kinds of sperm 

 relative to this set of chromosomes, namely male ,/ and female 

 A\ and male a and female a. These if equal in number and 

 equally free in their movements would give in fertilization: 



Male A -\- Female A = AA 

 " A -\- " a = Aa 

 " a + " A = aA 

 ci -\- a z=z aa- 



Or since A a and a A are alike the expression becomes A A -j- 

 2Aa -j- aa as the distribution, or again A -\- Aa -\- a as the 

 sum of possibilities of each chromosome pair. "Thus," Sutton 

 says^ "the phenomena of germ-cell division and of heredity are 

 seen to have the same essential features, viz., ]mrity of units 

 (chromosomes, characters) and the independent transmission of 

 the same. 



We must now return to the truly remarkable discoveries 

 made by Morgan and bis students and collaborators on nui- 

 tations in Drosophila and on the behavior of the mutant 

 attributes in heredity. These have consisted in showing that 

 such a relation between attributes and chromosomes as that 

 assumed in this relatively simple scheme worked out l)y 

 Sutton may be carried out in nnich detail both as to atti'i- 

 butes and chromosomes. An especially ingenious and fas- 

 cinating aspect of the theory as it has been elaborated large- 

 ly under Morgan's leadership, is that which shows tlu' 

 possibility that different parts of one and the same chromo- 

 some may correspond to several distinct attributes of the 

 adult; that these attributes may or may not be inseparabii- 

 from one another, and that when they are sej)arabK' tluy 

 may be transferred from one sex to Hie othir, presumably 

 by the transferrence of factors in one pai*t of a eliroinosomf 



