LINKAGE 



tance of 187 units lying to the right of stubby. 

 Klotz (1940) reported on linkage tests made 

 with veinless, lying approximately in the cen- 

 ter of this group. Veinless and honey are 

 linked with a crossover value of approximately 

 7.5 per cent (Clark, 1942). Veinless and stub- 

 by show no crossing over and are, therefore, 

 thought to be not linked. Veinless and lemon 

 show a linkage value of approximately 32,3 per 

 cent. Veinless and black shov/ a linkage value 

 of approximately 34.6 per cent. These data in- 

 dicate that the factors , veinless , honey , lemon, 

 and black, are located on the same chromosome. 

 Crossover percentages are 14 between black and 

 lemon, six between lemon and cantaloup, and 19 

 between cantaloup and honey (A. R. Whiting, 

 1939b) , Black is linked to stubby with a cross- 

 over value of approximately 30 per cent. Vein- 

 less and cantaloup are linked with approximate- 

 ly 30,6 per cent crossing over. Long and vein- 

 less show a linkage value of approximately 17,0 

 per cent. Long and cantaloup show a linkage 

 value of approximately 14,5 per cent. Inter- 

 ference is evident in the three point cross be- 

 tween cantaloup, long, and veinless, with the 

 ratio of coincidence being 0,537. Clark (1942) 

 reported data from six loci scattered along 

 about 70 units of the "cantaloup" group thought 

 to be near the center of the sex chromosome. 

 These data indicate that the black to lemon 

 region does not interfere with the lemon to can- 

 taloup region, but the cantaloup to honey re- 

 gion does interfere with the lemon to cantaloup 

 region. In testing the possibility that the 

 length (23.0) of the black-lemon region might 

 be responsible for the lack of interference, 



107 



