Genie and Non-genic Parts of the Chromosome 19 



the chromosomal membrane may be ruled out. The centromere may 

 be morphologically equivalent to parts for which the problem "genetic 

 or not genetic" exists. Normally it has morphological continuity, which 

 may be termed genetic. We must assume, in explanation of the cyto- 

 logical and cytogenetic facts discussed above, that the centromere 

 may multiply apart from chromosomal division or even be formed de 

 novo; also, that two centromeres may unite. The centromere is clearly 

 not concerned with what we understand as genie functions, that is, 

 wdth control of hereditary characters. In the same way the nucleolus 

 is not genie, although it is formed from a constant and self -perpetu- 

 ating part of a chromosome, and may play an important role in the 

 action of the genie material. A chromosomal membrane said to exist in 

 some ordinary chromosomes (Hirschler, 1942) and certainly present 

 in salivary gland chromosomes ( Kodani, 1942 ) cannot be called genie. 

 The ground substance, or kalymma, filling the spaces between the 

 chromosomal spirals — not generally accepted as existing — is ruled out. 

 There remain the chromonema proper with its visible differentiations, 

 the non-chromatic or little chromatic thread, and the chromatic knots, 

 knobs, and accretions generally called chromomeres and separated 

 into euchromatic and heterochromatic sections. 



There is no morphological differentiation between the chromo- 

 meres that could supply a clue to the genie or non-genic function of 

 the chromonema. Physically it is fibrous and more or less spiralized 

 according to the condition of the chromosome. Whether the chromo- 

 nema ever appears completely stretched is unknown. Even in a very 

 much stretched condition, as in the salivary chromosomes and in the 

 lampbrush chromosomes, it can still be stretched further experi- 

 mentally (Duryee, 1937), which might reach into the level of molecu- 

 lar unfolding. Only in the lampbrush chromosomes of the vertebrate 

 germinal vesicle, the longest chromosomes known (Gall, 1954), does 

 the chromonema seem maximally stretched; the single strand of the 

 synapsed homologues has the diameter of a large chain molecule. Butj 

 the electron microscope (Guyenot and Danon, 1953; Guyenot et al.A 

 1950) reveals the presence of two strands! As far as we know, thej 

 chromonema between the chromomeres is chemically not different 

 from the chromomeral section, at least qualitatively; in the lampbrush 

 chromosomes it contains diffuse DNA. Caspersson (1940) once main- 

 tained that different proteins are contained in the two sections, but we 

 have not heard much about this recently. Microscopically, it may 

 appear achromatic, but both nucleic acids are found microchemically, 

 which may signffy only a quantitative difference from the chromo- 



