SUMMARIZING REMARKS 147 



In all nucleic acid specimens the frequency of solitary and 

 coupled pyrimidine nucleotide units — and in some cases also that 

 of triplets — was determined. An example of such an analysis is 

 shown in Table 34. It will be seen that — in contrast to the first 

 observations^^ — no evidence emerged of a gross non-randomness 

 in the ability of the fraudulent analogue to substitute for thymine 

 within the polynucleotide chain. 



6. SUMMARIZING REMARKS 



a. Sequence characteristics common to all deoxyribonucleic acids 



Though the first application of the procedure for the differential 

 analysis of pyrimidine distribution served to demonstrate that 

 deoxyribonucleic acids from different species, even those show- 

 ing identical base composition, were vastly different with regard 

 to the alignment of their nucleotide constituents (Table 28), the 

 more important and interesting uses of this method bear on other 

 aspects of the sequence problem. These relate, in fact, to the 

 existence of sequential patterns that all deoxyribonucleic acids 

 examined heretofore appear to have in common. 



The first consequence of our studies may be the statement 

 that in no case can the nucleotide sequence be predicted from 

 the knowledge of the frequency of the individual constituents. 

 The discarded tetranucleotide hypothesis is a primitive example 

 of an attempt to make such a prediction; I have dealt with this 

 a long time ago^. This is, incidentally, quite similar to what one 

 would observe in a meaningful text: a certain letter may be par- 

 ticularly frequent; but this does not mean that it wiU occur, with 

 commensurate frequency, as a doublet. We shall probably find, 

 in general, that the symbols constituting a text are not arranged 

 at random, if this term is understood to refer to an alignment 

 governed only by the relative frequency of the elements, once 

 the requirement of large numbers is fulfilled. 



This brings up the problem of the non-randomness of the 

 nucleotide sequence in deoxyribonucleic acids which we have 

 discussed fully in a previous paper^i. Whether strict randomness 



References p. 159 



