34 Linkage Group II. 



In addition to modifying the wings, broken also affects the legs. The tibia on 

 the hind leg is strongly cur^•ed, or arched, with the concave side next to the femur, 

 and frequently the tarsi are shorter and swollen. 



Origin. — (M 66.) Broken appeared in acute stock. Only one broken fly was 

 observed, but others may have appeared. 



Comparison. — Superficially broken resembles the sex-linked character "crossvein- 

 less" in D. virilis and D. melanogaster (as noted above), and also a non-sex-linked 

 character in obscura, the stock of which has been lost (unpublished data of D. E. 

 Lancefield). It is not known how close the resemblance is in the latter case. 



LINKAGE DATA. 

 Detection of Linkage in Group II. 



Confluent and concave. — Four back-cross matings (V 675, 730, 740, 

 741) of males heterozygous for confluent and concave (in opposite 

 chromosomes) to homozygous concave females gave the following 

 counts: confluent 213, concave 213, confluent concave 0, wild-type 0. 

 A similar back-cross (V 752) using a male heterozygous for confluent 

 and concave, but this time in the same chromosome, gave : confluent 

 0, concave 0, confluent concave 46, wild-type 44. These experiments 

 show that confluent and concave are linked. 



Double with concave and confiuent. — Double has proved to be such 

 an unsatisfactory character to work with, on account of its tendency 

 to grade into normal, and its eff"ect on viability, that only a few 

 tests were made for linkage before the stock was discarded. These 

 are summarized below. Linkage between double and concave was 

 indicated by the F2 count from a cross of concave by double. This 

 consisted of 118 wild-type, 33 concave, 33 double, without any con- 

 cave doubles (P 19, 30, 31). Similarly, linkage between double 

 and confluent was indicated by the progeny of matings (E 998, 

 E 1001) between confluent and double, using double females and 

 males heterozygous for confluent (dominant) and double. These 

 gave: confluent 142, double 113, wild-type 0, confluent double 0. 

 The 5 wild-type flies in the latter case are assumed to be genetically 

 double. 



Confluent and broken. — Linkage between these two characters 

 was shown by the usual back-cross test, using heterozygous males. 

 Two such matings (M 291, M 292) gave: 23 confluent, 27 broken, 

 and no wild-type or confluent broken flies. 



Cross-over Values in Group II. 



Confluent and concave. — Two back-cross matings (experiment 54) , 

 using females heterozygous for the two genes in opposite chro- 

 mosomes, gave 123 non-cross-over flies, and 90 cross-overs. This 

 gives a cross-over value of approximately 42 per cent, without any 

 correction for double crossing-over. 



Confluent and double. — Six back-crosses (E 931, E 947, E 948, 

 E 1032, E 1033, E 1034), using heterozygous females from confluent 



