SOME REMARKS ABOUT THE DISTANCE 



BETWEEN THE GENES IN DROSOPHILA 



MELANOGASTER 



Hv i)axh:l rosijx 



KMFPAN, SWEDKN 



THE epoch-making theory formulated by Morgan and his co- 

 workers BiuDGEs, MuLLER, Stuutevant a. o. to explain the 

 coupling-behaviour of the genes in Drosophila inelanogaster may now 

 be said to be generally accepted among geneticists. Goldschmidt 

 (1917), however, has recently attacked it, and Castle (1919) has later 

 tried to formulate a new theory to explain the phenomena of coupling. 

 In the following an attempt is made to add a few remarks on the 

 distance between the genes in the chromosomes. 



It has been shown by Morgan and his co-workers that the genes 

 in Drosophila melanogaster are placed in a row in a definite order, 

 and that this order always remains the same at crossing over. A gene 

 seems therefore capable of combining only with two genes, one of 

 higher place number in the chromosome and one of lower place number. 

 Thus the interchange of chromosome parts can only take place 

 between corresponding groups of genes. Castle, in his attack on the 

 Morgan theory, emphasizes among other things that a purely mecha- 

 nical theory cannot explain this behaviour. It seems necessary to 

 assume the play of certain forces in order to reach an understanding 

 of the interchange of chromosome parts in the above mentioned 

 manner. Weinstein (1918, pag. 149) seems to allude to something 

 similar in the following: »If, therefore, the determinations of coin- 

 cidence in this paper are valid and comparable with each other, they 

 seem to show, that the twisting of the chromosomes during crossing 

 over is loose; or, if it is tight, that the distance between the places 

 of crossing over depends on other conditions than the mere tension 

 due to twisting . 



Federley (19Ki) explains the peculiar phenomena seen in the 

 Pijgacra bastards on the basis of the assumption that the conjugation 

 of the chromosomes fail to appear because of lacking affinity. It 

 seems therefore permissible to make the assumption that affinity plays 



