44 Linkage Group IV. 



Pinched (P). (Plate 3, Figure 11.) 



Description. — Pinched is a dominant. In heterozygous flies the anterior cross- 

 vein is shortened, so that the third and fourth longitudinal veins are almost pinched 

 together, and a characteristic short branch projects from the fourth vein below the 

 first basal cell. Homozygous flies exhibit these same features, and in addition the 

 effect often extends to other veins; the posterior cross-vein may be shortened and 

 may lie diagonally between the fourth and fifth longitudinal veins and the latter 

 may be broken or shortened. No difficulty is experienced in classifying pinched 

 flies, but considerable variation is exhibited in both heterozygous and homozygous 

 individuals, and it is not possible to separate them in a mixed culture. The pinched 

 factor does not have the completely lethal effect frequently exhibited by dominants 

 when homozygous. It does, however, have a very detrimental effect on the viability 

 and fertility. 



Origin. — (L 252.) Pinched appeared in a culture carrying hump, and the pinched 

 factor shows complete linkage to that for hump. Evidently the mutation occurred 

 in the chromosome carrj'ing the hump factors, for the two have remained inseparable; 

 consequently all homozygous pinched flies are hump. It should be noted that 

 although pinched is always accompanied by hump, the converse is not true, for 

 hump arose independently some months before the appearance of pinched and the 

 original hump stock is free from pinched. The two mutations may have occurred 

 in the same locus, producing allelomorphic characters, but the characters bear no 

 relation to each other, one affecting the thorax, the other the wings, and probably 

 merely constitute a case of complete linkage. 

 This is made all the more probable by the 

 apparent absence of crossing-over between 

 either of these characters and acute (see 

 below) . 



Hump (hp), (Figure 11.) 



Description. — Hump is characterized by 

 an unusually arched and shortened thorax 

 and a dark, glossj^ body-color somewhat like 

 that of forked. The males may also be dis- Fig. ii. — Hump, 



tinguished by the absence of color in the 

 testes, which in normal flies are orange red. It has excellent viability and fertility. 



Origin. — Hump was first observed in a"normal" stock descended from flies ob- 

 tainedf rom Dr. Roscoe Hyde, and taken from astock originally secured in Terre 

 Haute, Indiana. 



LINKAGE DATA. 



Detection of Linkage in Group IV. 



Acute and pinched. — Since pinched is a dominant character, males 

 heterozygous for acute and pinched were back-crossed to acute 

 females. Two such matings (L 497, L 505) gave the following count : 

 acute 84, pinched 100, wild-type 0, acute pinched 0, which shows 

 that acute and pinched are linked. 



Acute and hum-p. — In this case the preUminary indications of 

 hnkage were obtained from the F2 of a mating between acute and 

 hump. This gave (L 561): wild- type 68, acute 27, hump 16, without 

 any acute hump flies. 



