A NEW GENE IN THE SECOND CHROMOSOME OF 



DROSOPHILA AND SOME CONSIDERATIONS 



ON DIFFERENTIAL VIABILITY. 



C. B. BRIDGES AND A. H. STURTEVANT. 



Morgan and Lynch (BiOL. BULL., '12) and Morgan (Science, 

 '12) have reported the linkage relations of two non-sex-linked 

 genes, black and vestigial. 1 Morgan considered these two genes 

 as lying in a "second chromosome," the first chromosome being 

 the sex chromosome. He showed that in the female there was 

 a considerable amount of crossing over between these two genes, 

 but in the male there was none at all so far as the data showed. 



At the time when this linkage between black and vestigial was 

 first observed w T e were engaged in a systematic search for linkage 

 between non-sex-linked genes in Drosophila. One of us (Bridges) 

 had already observed in the F 2 generation of a cross of black by 

 curved 2 that no black curved flies appeared. We interpreted 

 this case as one of linkage of such a strong order that no crossing 

 over had taken place. On the basis of this linkage we concluded 

 that curved was in the same chromosome as black, that is, in a 

 41 second chromosome." The similar work of Morgan on black 

 and vestigial showed that the non-appearance of the double 

 recessive in a case in which two second chromosome recessives 

 entered the FI from opposite parents, could be explained on the 

 basis of lack of crossing over in the male. The present paper 

 shows that the same explanation applies to the case of black by 

 curved, and further deals with the determination of the amount 

 of crossing over in the female between the black and the curved 

 loci. 



An individual heterozygous for two allelomorphic pairs as 

 AB, ab may form four kinds of gametes, namely AB, ab, Ab, and 



1 Vestigial was at that time called wingless. 



"Curved" a wing mutant discovered by Bridges is characterized by the thin 

 texture of the wings which are held out widely from the body and curved. This 

 and other mutants are shortly to be described in detail by Morgan and Bridges. 



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