IN THE SECOND CHROMOSOME. 319 



Pr Cjir . „__ , , Cut C m 



7 — - — - — , from 677 was mated to a cross-over male, t-^^-^ ' 



^ Pt ^ ' b p, c 



from 678. The resulting wild-type offspring were r^ — —. A 



" Pr Cjjr 



female of this constitution, in culture 718,gave4..3 per cent crossinK-ovor 

 between pr and c, none between 6 and yr or between c and vxr. The 



same general method was followed in making up seven other "^ , — 



^ ttr 



females. The same Cm c chromosome was present in all these 

 females, but Cii r from different sources was used. The results from 

 these females are given in tables 15 and 10 and the fifth line of figure 1. 

 These data agree with those obtained from Cm C'//,, except 

 that Pr c shows a slight rise (from 1.1 to 2.9). Owing to the statistical 

 difficulty of handling such small ratios it is not possible to say whether 

 this difference is significant or not until more data can be collected. 

 The point is of interest in its bearing on the mechanism of the action 

 of Cm and Cur, but must be left unanswered for the present. 



The second brood data here presented for -^^ are entirelv 



Cllr 



inadequate for the purpose of detailed comparison with first brocxis. 

 They do, however, show an increase for pr c over the Cm C^r 

 second broods (from 1.2 to 2.2). 



HOMOZYGOUS dir. 



We have seen that heterozygous C^r greatly decreases crossing- 

 over in the region from purple to speck, but does not ai^preciiibly 

 affect the region from star to purple. The data now to be presented 

 show that homozygous Cjir gives a value for purple speck that is 

 very close to that found in "normal' ' flies, but again does not influence 

 the region from star to purple. 



It has so far not been found possible to obtain a chromosome con- 

 taining Cii r with vestigial or curved, since heterozygous ('/; , practi- 

 cally prevents all crossing-over in the region in which these three genes 

 are located. For this reason none of the data on homozygous Cn r 

 deal with loci between purple and speck. 



HOMOZYGOUS C//. WITH Cm. 

 In the course of the experiments with Cur a chromosome of the 

 constitution ♦S' h pr Cnr Sp was obtained.^ When males with this 



Pr O/ r *p 



1 This chromosome was derived from culture 570 (see p.314). in which was a fcmalo ^ ^ Or *p' 



A cross-over in this female gave a 6 Pr Cn r «p chromosome. This chromosome, or a dcriv»uve 

 of it, since it had perhaps been passed through a b ;,^ c'nl » ^^'"'^'^' ^'^ '''""^ oppo«t« •t«r 



( — ) in the females of cultures G9G and 099a. The chromosome rofcrrcd to a»x>v« 



\ Pr tn T Sp / ■ I. t 



(5' h Pr Cn r Sp) was produced by crossing-over in these females and was kept inUct thcns»ft4sr 

 by breeding from males heterozygous for it. in which no croaaing-over occurred. 



