CHROMOSOMES 

 AND GENES 



The morphology and the biochemistry of the chromosome have taught 

 us a number of important facts. But they have failed thus far to give 

 a clear answer to the question: What is the genie material in the 

 chromosome? Perhaps the question itself was based upon a wrong, 

 preconceived idea. Saturated as we are with the clear, unassailable 

 facts of Mendelian inheritance, we are conditioned to thinking in 

 terms of discrete units which can be shifted and recombined like 

 dice in a throw, never losing their identity in a kind of splendid 

 isolation. Therefore, it is a kind of natural instinct to look in a 

 chromosome for these discrete units, the genes, and this desire 

 prompted our question about the genie part of the chromosome. 



Optimistic observers more than once have claimed to have seen 

 the genes. About twenty years ago Belling, a brilliant observer and 

 a keen thinker, took me with solemn ceremony to his microscope to 

 show me the gene. He had succeeded in staining distinctly within 

 some big chromomeres a tiny but clearly visible central dot which 

 he considered to be the gene finally made visible. The number of 

 geneticists is not small who talk of the bands in the salivary chromo- 

 somes as genes and obviously are convinced that these are the real, 

 visible genes of classic Mendelism, though numerous facts already 

 mentioned or still to be mentioned are opposed to such oversimplifica- 

 tion. Recently much smaller structures have been seen in the bands 

 with the electron microscope and have been hailed as the real genes. 



If we try to forget this instinctive quest for the visible hereditary 

 unit and face the facts described in the search for the genie material 

 in the chromosomes in an unprejudiced way, we cannot help feeling 

 that the facts point in another direction. They seem to indicate that 

 the chromosome is not an assembly of independent units but a kind 

 of microorganism in which all parts are needed and interacting in 

 some way, so that the entire chromosome, not definite parts, has to 

 be called the genie material. Just as the theory of the separate units, 

 the genes, was not derived from cytological facts but from genetic 

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