THE REDUPLICATION HYPOTHESIS AS 

 APPLIED TO DROSOPHILA 



Dr. a. h. sturtevant 



A number of papers developing the reduplication hy- 

 pothesis of linkage have recently appeared in the Journal 

 of Genetics. They are based almost entirely on the 

 experiments of Gregory ('11) on Primula and of Punnett 

 ('13) on the sweet pea. The data are not entirely satis- 

 factory because of the relatively small number of genes 

 involved, and because in most cases the gametic ratios can 

 be only approximately determined. This is due to the 

 fact that most of the data concern F 2 counts, from which 

 gametic ratios can not he calculated directly. In Gregory's 

 best case a much more satisfactory method was followed— 

 the heterozygous plants were tested, not by mating to 

 others of their kind, but by crossing with plants recessive 

 with respect to all the genes involved, which gives the 

 gametic ratio directly. In this case, however, we have 

 only a relatively small series of data involving as many as 

 three pairs of linked genes. It is obvious that from such 

 data no adequate test of the reduplication hypothesis can 

 be made. 



The phenomena of linkage have been very extensively 

 studied, by Morgan and others, in the fly Drosophila. In 

 this animal there are many genes belonging to the same 

 linkage groups, and these have been studied on a large 

 scale. In the case of the sex-linked group there is never 

 any difficulty in calculating the gametic ratio from F 2 

 results, since the F 2 males from any cross always give it 

 directly. I have recently published a paper (Sturtevant, 

 '14) giving a complete summary of the published results 

 obtained from studies of the linkage of these genes. In that 

 paper I have adopted the chromosome explanation of link- 

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