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Germinal Changes in the Bar-Eyed Race of Drosophila 

 During the Course of Selection for Facet Number.* 



Charles Zeleny, University of Illinois. 



In recent discussions two explanations of the effect of selection have 

 been offered. According to the tirst of these the results obtained are due 

 merely to a sorting out of differences existing in the stock at the begin- 

 ning of selection. According to the second, new germinal differences 

 arise during the course of selection. 



Among those who admit the continued production of new germinal 

 differences there is a disagreement as to the manner in which the ger- 

 minal changes occur. Some hold the view that the changes consist wholly 

 of the production of new unit factors or genes. Others on the contrary 

 believe that gradual change in the original genes is the principal mode 

 of action and even that selection itself is an efficient determiner of the 

 direction of such variation. 



It is my intention to mention briefly some of the results bearing on 

 this problem which have been obtained in the course of selection for 

 facet number in the bar-eyed race of Drosophila ampelophila. 



Bar-eye appeared in 1913 as a single mutant male in a full-eyed 

 stock. This male gave rise to the bar-eyed stock in v/hich the faceted 

 region of the eye is bar shaped and the facet number is reduced from 

 one thousand or more to about one hundred. An analysis of the hered- 

 itary behavior of bar-eye shows that it differs from full-eye in a single 

 sex-linked genetic factor which acts as an incomplete dominant, the het- 

 erozygous condition being intermediate between bar and full-eye. My 

 stock was obtained from Professor T. H. Morgan in January, 1914, and 

 since that time experiments on selection for high-facet and for low-facet 

 number have been in progress, but not in a continuous series because of 

 loss of the lines on several occasions. In these experiments it has been 

 shown that selection for low-facet and for high-facet number is effective, 

 and low-bar, high-bar, emarginate eye and full eye have been produced 



Contributions from the Zoological Laboratory of the University of Illinois, No. 110. 



