152 THE SECOND-CHROMOSOME GROUP 



STOCK OF VESTIGIAL. 



Since vestigLal, like balloon, appeared in the truncate stock, the 

 vestigial flies were often at the same time truncate, though these could 

 not be distinguished by inspection from the simple vestigials. By out- 

 crossing and extraction a stock was obtained which seemed to be free 

 from truncate (as judged by the absence of truncates among the not- 

 vestigial flies of certain Fi and F2 cultures). The balloon 'mutation 

 which had appeared in the truncate stock just before the occurrence of 

 vestigial was even more difficult to eliminate and occasionally cropped 

 out in the early experiments in which vestigial was used. 



INHERITANCE OF VESTIGIAL. 



In out-crosses to wild the vestigial appeared to be completely reces- 

 sive. In F2 the vestigials reappeared in much less than a quarter of 

 the flies, due to the practice of using mass cultures and to the rather 

 poor feeding methods of that time. Reciprocal crosses gave the same 

 results in Fi and F2, so that the gene was known to be not sex-linked. 



Lutz (1913) made a biometrical study of wing-length and found that 

 the wings of flies heterozygous for vestigial are slightly but actually 

 shorter than the wings of ^"ild flies. Also, the ratio of wing-length to 

 femur-length was less, showing that vestigial is not completely reces- 

 sive. It is known in other cases also (see Morgan and Bridges, 1913) 

 that characters that to simple inspection are completely recessive 

 really are influencing the character of the heterozygous individuals. 



CHROMOSOME CARRYING VESTIGIAL. 



At this time the only case of autosomal linkage known in Drosophila 

 was the observation by Bridges that no black curved flies had appeared 

 in the Fa of the cross of black by curved (Bridges and Sturtevant, 

 1914). Following this, a concerted testing of the linkage relations of 

 all the known autosomal mutations was carried out. One of these 

 tests, made by Sturtevant and by Miss Clara J. Lynch, showed that 

 in the F2 of the cross of black by vestigial no black vestigial flies 

 api)eared. Both of these cases were put down as very close Unkage, 

 "complete repulsion," since it was not yet known that there is no 

 crossing-over in the male whereby this result would be obtained, even 

 though the crossing-over in the female were very free. That crossing- 

 over actually had occurred was shown by the results of mating some 

 of the F2 black by some of the F2 vestigial flies. In one of these F3 

 cultures some black flies occurred, which meant that at least one of 



the vestigial parents had been heterozygous for black, ^ — - , the b v. 



Vn 



a 



