VERMILION-DEFICIENCY. 



By CALVIN B. BRIDGES. 



{From the Zoological Laboratory of Columbia University, New York, and the 

 Carnegie Institution of Washington.) 



(Received for publication, April 18, 1919.) 



CONTENTS. 



Summary 645 



Origin and lethal action of vermilion-deficiency 646 



Linkage tests of the extent of the deficient region and the disturbance 



in crossing over in adjacent regions 650 



Relation between vermilion-deficiency and vermilion-sable duplication 654 



Haploid and cytological tests of the extent of the deficient region 655 



Dominant action of deficiencies 655 



SUMMARY. 



In May, 1916, a culture of Drosophila melanogaster showed that a 

 new sex-linked lethal had arisen. The linkage relations indicated that 

 the position of the lethal was in the neighborhood of the sex-linked 

 recessive "vermilion," whose locus in the X chromosome is at 33.0. 

 When females heterozygous for the lethal were outcrossed to vermilion 

 males, all the daughters that received the lethal-bearing chromosome 

 showed vermilion eye- color, though, from the pedigree, vermilion was 

 known to be absent from the ancestry of the mother. The lethal 

 action and the unexpected appearance of vermilion both suggested 

 that this was another instance of the phenomenon called "deficiency;"^ 

 that is, the loss or "inactivation" of the genes of a section of the X chro- 

 mosome. The lethal action would then be due to the deficient region 

 including one or more genes necessary for the life of the individual. 

 The appearance of vermilion in females carrying only one vermilion 

 gene would be explainable on the ground that the dejacient-bearing 



^ Bridges, C. B., Genetics, 1917, ii, 445. 



645 



