CHKOMOSOME STUDIES 259 



of accounting for some of the phenomena of couphng and re- 

 pulsion and the deviations from this, i.e., failures of linkage. 

 Janssens's ('09) theory of the chiasmatype is the first explanation 

 that has been offered. Phenomena of coupling and repulsion 

 ba.ve been observed by Bateson and Punnett ('11), Correns, 

 Baur, Emerson, East, Trow, and especially by Morgan and 

 his students in their bred Drosophila ampelophila. In their 

 experiments the last mentioned authors have found that certain 

 groups of characters, usually carried together, occasionally be- 

 come broken into two groups. A specific case is afforded by 

 the results obtained when a gray, red-eyed female is crossed with 

 a yellow, white-eyed male (Morgan '13, p. 88). The factors 

 for gray body and red eye are usually carried together with 

 the sex determining chromosome, their allelomorph yellow body 

 and white eye likewise in a sex chromosome. The offspring 

 in Fi are all gray-bodied and red-eyed in both sexes. In the 

 F2 generation the expected results, assuming for the moment 

 free interchange of the factors for gray and yellow body and 

 for red and white eye, would be 4GR 9 : IGR cf : IGW d' : 1 YR cT : 

 lYWcf. But this ratio is not realized. The results obtained 

 arel70GR9 :84GRcf : IGW cT- :lYRc^ :84WYc^, which show that 

 there is a tendency for the factors that entered together, gray 

 body and red eye, and yellow body and white eye, to remain 

 together. By these numbers in F2 it may be seen that coupling 

 was not complete but failed in the proportion of 1 : 84, in other 

 words the chances are 84: 1 that the factors entering together 

 will remain together. Now, it seems possible that such a small 

 departure from normal coupling as 1 : 84 might be explained by 

 an occasional break in the V sex chromosome at the apex. Ste- 

 vens ('08, figs. 61, 65-73) gives two V-shaped sex chromosomes, 

 one a normal V and the other carrying attached to its apex a 

 rod-shaped element, the nature of which is not clear. That 

 V's may be formed by the fusion of non-homologous rods by 

 their proximal ends and also that rods may be formed by the 

 breaking of a V at its proximal end, the apex, is to be inferred 

 from the presence of a V and its rod-mates in one and the same 

 individual (figs. 196-199) . The same may reasonably be expected 



JOURNAL OF MORPHOLOGY, VOL. 27, NO. 2 



