Genie and Non-genic Parts of the Chromosome 57 



genie material. My conclusion from the facts available today is that 

 the protein of the chromonema is the genie material proper, but that 

 it requires the linked DNA molecules for self-duplication. Thus the 

 combination of both is the basis for genie action. We shall have to 

 return many times to this basic and intriguing problem. 



C. HETEROCHROMATIN 



In the search for the genie material of the chromosome we have 

 neglected thus far two other constituents of the chromosome. One is 

 the nucleolus, a structure for which nobody would claim genie prop- 

 erties. It is cyclically destroyed and rebuilt and is quantitatively more 

 variable than could be assumed for genie material. Thus there are 

 chromosomes without a nucleolus, which is formed only in one or two 

 pairs of a genome. There are also chromosomes (amphibian oocyte) 

 in which numerous nucleoli are imbedded. The major part of the 

 nucleoli consists of ribonucleic acid, and it is generally assumed that 

 this has to do with protein synthesis in the cytoplasm. Thus nucleoH 

 are chromosomal structures concerned with the non-genic functions 

 of the chromosomes. They will be taken up again in the discussion of 

 the relation between nucleus and cytoplasm. 



That part of the chromosome which is called heterochromatin 

 shows a number of very remarkable properties. There is a large 

 literature on the subject, both in cytological and genetic work (good 

 reviews: Pontecorvo, 1944; Hannah, 1951; Barigozzi, 1950fl; cytological 

 details: White, 1945; Smith, 1952; genetical study: Goldschmidt, 

 Hannah, and Piternick, 1951). Not all the numerous facts known fit 

 together, and contradictions are frequent. It is hardly possible yet to 

 develop a completely satisfactory theory of heterochromatin. How- 

 ever, one thing may be said with certainty: heterochromatin must play 

 a considerable role in the history of the chromosomes and in their 

 function, and an important but unorthodox genetic role is expected. In 

 order to reach more specific conclusions we shall group the genetic 

 and cytological facts so that their individual meaning comes out 

 before we attempt a synthesis of all the facts. In doing so we shall not 

 emphasize difficulties and discrepancies, but rather shall try to elabo- 

 rate the positive, constructive parts of our knowledge. 



a. The cytological aspect 



The original meaning of the term "heterochromatin" was purely 

 cytological (Heitz, 1929). It meant the existence of chromosomal 

 regions differing from the others by their staining, according to the'n'i pV>\ 



