OF MUTANT CHARACTERS. 



291 



These tests brought out the interesting point that in crosses in 

 which a recessive and a lethal are in opposite chromosomes ( J , 



the percentage of the recessives in F 2 is a constant value 33.3, 

 irrespective of how much or how little crossing-over there is between 

 the two loci. Thus, the recessives purple, plexus, and speck are at very 

 different distances from the locus of the lethal, yet the percentages of 

 appearance of all these is practically the same (p r = 37.0, p r = 34.0, 

 s p = 35.3, though slightly higher than the expected value of 33.3. 



TABLE 135. The offspring from pairs of black curved flies from Z// a stock 



/bp T +cp x * p 



[All flies were black curved and showed also the subdivisions in the table.] 



TELESCOPE (0- 



(Plate 7, figure 6.) 



ORIGIN OF TELESCOPE. 



In determining the locus of the sex-linked mutant "crooked bristles" 

 (locus 38.0, allelomorph of furrowed) several back-cross tests were 

 made of females carrying vermilion, crooked, sable, and garnet in one 

 X, and only wild-type genes in the other. One of these tests gave 

 slightly less than a quarter of the flies with "telescope" abdomens 

 (2735, December 27, 1915). 



DESCRIPTION OF TELESCOPE. 



The abdomens of the "telescope" flies tend to retain the drawn-out 

 appearance that freshly hatched flies have. The segments are slightly 

 separated from one another instead of overlapping. The pigmenta- 

 tion and chitinization of the abdomen remain weak and there is a wet 

 (glazed) appearance to the entire surface of the body. The wings droop 

 at the sides and diverge, this character being very useful for identifi- 

 cation. Each band is sunken at the middle, with slightly raised edges. 



INHERITANCE OF TELESCOPE. 



That this character was not sex-linked was seen at once, since in 

 the culture in which it was first found it appeared in females as well 

 as males and showed no linkage to any of the four sex-linked characters 



