BRIDGES 



The writer has two articles in press, 

 one dealing with the technique and 

 the general morphological characters 

 of the salivary chromosome, the sec- 

 ond, a detailed study of the X-chro- 

 niosome from which the drawing pre- 

 sented herewith was taken. Similar 



163 



studies of the autosomes have been 

 under way for some time, and a num- 

 ber of students are at work on various 

 cytological and genetic problems 

 opened up by the new method of at- 

 tack. 



\^ 



The Bar "Gene" a Duplication 



CALVIN B. BRIDGES 



Reprinted by publisher's permission from Sci- 

 ence, vol. 83, 1936, pp. 210-211. 



The facts of a field of scie?ice are similar to the pieces of a child's 

 i?2terlocking puzzle. All have their place, and it is usually if not al- 

 ways impossible to get them to go together out of seqeunce. On the 

 other hand, zuheji properly arranged, they fit very snugly indeed, 

 and present a complete figure. This paper by Bridges combines the 

 techfiique described by Painter (page 161) with the kifid of i?ives- 

 tigation brillia?itly carried out by Creighton and McClintock (page 

 155) and gives as a residt a more detailed and iji formative explanation 

 of the proble?n first investigated by Sturtevant (page 124). This is 

 the way a science grows, bit by bit, and fact by fact. 



The nature of the bar gene has 

 been the subject of extensive investiga- 

 tion and speculation since February, 

 1913, when Tice ^ found this reduced- 

 eye mutant as a single male in the 

 progeny of normal-eyed parents. The 

 eye-reduction behaves as a sex-linked 

 dominant, with a locus at 57.0, and has 

 been one of the most important of all 

 the sex-linked characters of D. me- 

 lanogaster. A remarkable peculiarity 



of the mutant is that occasionally the 

 homozygous stock gives rise to a fly 

 indistinguishable in appearance and ge- 

 netic behavior from wild-type.^ More 

 rarely the stock gives rise to an even 

 more extreme reduction in eye-size, a 

 type which was called Ultra-Bar by 

 Zeleny,^ who found it. 



1 Tice, S. C, Biol. Bull. 26:221-51, 1914. 



2 May, H. G., Biol. Bull. 33:361-95, 1917. 

 3Zeleny, C, Jour. Exp. Zoo/. 30:293-324, 

 1920. 



