Genie and Non-genic Parts of the Chromosome 31 



together by electric forces, by binding calcium or magnesium ions. 

 It is concluded that the chromosome consists of macromolecular 

 complexes of nucleoprotein, linked by bridges of divalent ions (Ca, 

 Mg, or both) as well as by the interactions making for insolubility 

 at moderate ionic strengths. We do not think that these findings 

 change anything in our discussion of the genie material. 



The insight gained into the nature of the genie material in the 

 chromosome from direct biochemical study is virtually nil thus far, 

 and we must rely on indirect information from morphology, genetics, 

 and general cytology. Most of such work deals with the theory that 

 DNA is the genuine genie material (as opposed to the proteinic 

 chromonema or genonema). Thus we must consider critically the 

 data in favor of DNA. 



b. DNA as genie material 



The first and main support of the claim that DNA is the ex- 

 clusive genie material is the constancy of the quantity of DNA in 

 the nuclei of cells of a given species and its absolute dependence 

 upon the number of chromosomes within the species. The develop- 

 ment of more (Caspersson, 1939 ff.; see 1950) or less (Pollister and 

 Ris, 1947) complicated methods of measuring this quantity by light 

 absorption has led to remarkable information (work initiated by 

 Boivin, 1947, and Mirsky and Ris, 1947, followed by Pollister, Schra- 

 der, Leuchtenberger, Alfert, and Swift; see review by Swift, 1953). 



aa. Quantitative constancy of DNA 



The work started from experiments with bacterial transformation 

 in which a specific DNA supplied in the medium seems to become 

 incorporated into the genetic system. On the theory that a genie 

 constituent should show the same quantitative relationship per nu- 

 cleus as does the chromosome number, Boivin ( 1947 ) determined the 

 amount of DNA in tissue nuclei. The amount was found to be con- 

 stant, and the amount in haploid sperm cells approximately half of 

 it. Boivin as well as Mirsky and Ris worked this out in great detail 

 for a variety of cells with the same result, but there were some 

 discrepancies which could not be accounted for, because these 

 measurements were made by chemical analysis of millions of cells. 

 The introduction of optical methods permitting measurement of single 

 nuclei showed the cause of the discrepancies. 



Such measurements by these and other authors revealed that the 

 quantity of DNA in many nuclei approximated a 1:2:4 ratio. Jacob] 



