48 Linkage Group V. 



LINKAGE DATA. 



Considerable difficulty is encountered in using the characters of 

 this group in combination for linkage tests, because some are irregular 

 in appearance, and all but ruffled affect the wings. Branched is 

 unsatisfactory because it does not always manifest itself; interrupted 

 causes difficulty for the same reason, and also because it prevents 

 the detection of approximated, in some cases, by removing most of 

 the posterior cross- vein; and finally fused often interferes with the 

 identification of approximated by eliminating the anterior cross-vein. 

 For these reasons it is usually necessary to classify some of the flies 

 as doubtful, with the result that cross-over values are not accurate. 



The new character "ruffled" was obtained too recently to permit 

 of extensive use in linkage tests, but it promises to be very valuable 

 for this purpose, since it does not affect the wings. 



Detection of Linkage in Group V. 



Branched and fused. — The linkage of these two characters was 

 revealed when heterozygous males were back-crossed to fused 

 females (branched being a dominant). This type of mating gave 

 (E 581, E 607, E 615): 140 fused, 199 branched, and 5 (somatically) 

 wild-type offspring — the latter almost certainly being genetically 

 branched. (See above under "branched.") 



Branched and approximated. — Linkage in this case was likewise 

 detected by back-crossing heterozygous males (E 1123, E 1139), 

 from which the following offspring were obtained: branched 115, 

 approximated 162, branched approximated 0, and wild-type 9 

 (the latter presumably genetically branched). 



Fused and interrupted. — Linkage in this case was indicated by the 

 F2 results following a cross of fused and interrupted. The counts 

 here were (E 560, E 569) : wild-type 148, fused 62, and interrupted 84, 

 with the double recessive class lacking. 



Interrupted and approximated. — These characters were shown to 

 be linked by the following back-cross, a heterozygous male, which had 

 received both mutant genes from one parent, mated to a double reces- 

 sive female, gave 51 interrupted approximated flies, 49 wild-type, two 

 approximated (genetically interrupted also), and no interrupted. 



Branched and ruffled. — Back-crosses of heterozygous males were 

 used to detect the linkage in this case also. Two of these (M 325 

 and M 327) gave 67 branched, 38 ruffled, 4 wild-type (presumably 

 genetically branched), and no branched raffled. 



Cross-over Values. 



Fused and interrupted. — Data involving these two characters are 



subject to error, due to the irregularity of interrupted and the low 



viability of fused. The results of 6 back-crosses are given under 



experiment 64. It is evident that a large proportion of the genetically 



