XLIII 



BIOLOGICAL ASPECTS OF THE QUANTUM THEORY 

 OF RADIATION ABSORPTIONS IN TISSUES 



John W. Gowen 



Department of Animal and Plant Pathology of The Rockefeller 

 Institute for Medical Research, Princeton, N. J. 



The amplification of the mendelian theory by other researches shows 

 the chromosomes (58) to contain the specific determiners of the inherit- 

 ance, the genes, arranged Unearly with regard to each other. The total 

 effects of these genes control the development and maintenance of all 

 parts of the adult organism. Individually considered, however, the 

 effects are quite specific. A gene may alter the eye color or reduce the 

 \vings of Drosophila but otherwise show little to indicate its presence. 

 One may make a harmless black spot under the wing joint (58), while 

 another may cause a focal melanosis (24) in the leg joints ultimately 

 resulting in the death of the fly. Organs vital to the fly may be altered 

 in shape and structure as the result of the presence of specific genes. 

 And finally a large class of genes exists in which each one of them under 

 the proper conditions, when dominant or homozygous, causes the death 

 of the organism containing it in its cells. 



The distribution of these different types of genes is apparently at 

 random within the cell chromatin. A gene whose function it is to assist 

 in producing a certain eye color may have as its known neighbor a gene 

 which causes death or a gene which acts upon the legs, the wings, or 

 any other part of the body. Random chance alone seems to determine 

 the spatial order of the different types of genes within their linear order. 

 A given gene's position within this linear order is ordinarily fixed. For 

 every known gene difference at least two genes capable of producing 

 markedly different effects on the same organ, or less frequently on 

 different organs, may occupy the same position, locus, within the chromo- 

 some. Dividing the genes into groups according to the broad categories 

 of character changes which they produce and according to their location 

 within the chromatin structure, we have genes which produce dominant 

 or recessive characters, dominant or recessive lethals. These may be 

 autosomal or sex-linked. The presence of the recessive lethals is well 

 proved by the study of their genetics. The fact of dominant lethal genes 

 has less, though growing, evidence in its support. 



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