THE CENTRAL PROBLEMS OF TIIK BIOCHEMISTRY OF CELL DIVISION 479 



expect to find two generations in existence at the same time. The double 

 cliromosome is not always strictly double; during the period of develop- 

 ment it contains two sets of DNA but may consist of a complete parent 

 chromosomal unit and an incomplete daughter chromosomal unit. 



This generative scheme of chromosome reproduction seems rather 

 comjilicated, but no niori' so than the better known case of the reproduction 



END DIVISION 



END INTERPHASE 



END /NAETA PHASE 



Fui. I. Diayrani ol a possihlc ^tncrativc- plan of iipioiluction ot the- whole- 

 chromosome. Chromosome is represented as genetically duplex at all times. 

 DN.A (symbolized as double helix) replicates durinji; interphase and is simultaneous 

 joined to histone, which may be synthesized at the same time or earlier. Other 

 chromosomal proteins (P) are synthesized or incorporated later. In this version, 

 the complete reproduction of a chromosome strand, including the reproduction 

 and splittinji; of the kinetochores (K) is not completed until anaphase. If this is so, 

 the division will sind one " old "' ami one " new " straiul to each pole. I f the rtpro- 

 duction is completed before anaphase, the four units may split at random. 'The 

 reproduction of the nucleolus takes place during division; the old nucleolus breaks 

 down at prophase and two niw iiuekoli appear at anaphase. 



of bacterial \iriKses. There, tlie parent "soma" seems to be rejected 

 entirely, the DNA reproduces to conceive many new units, and the 

 complete imits are later de\ eloped aroimd the DNA "seeds". To imagine 

 that the whole bacteriophage reproduces in a single steji would now seem 

 absiu'd. 



These questions concerning the reproduction oi the whole chromosome 



