3. Chromosome 7 linkage data - Professor A. C. Fraser made the following field plantings last spring and marked the seedlings. I assume all responsibility for the records on the mature plants and the following summary of the results (table 1).
|Table 1||+ + +/in v5 gl|
|552 438||1 11||18 20||2 12|
Recombination percentages: in-v5 2.4, v5-gl 4.8
Ratios: 573+ : 481 in, 593+ : 461 v5, 585+ : 469 gl
Percent non-germination of In seeds 20.6, of in seeds 28.4.
Fraser in News Letter 1938 (p. 11) reported in-V5 = 4.3% V5-gl = 12.2% where n = 1017 and in News Letter 1940 (p. 14) in-V5 = 6.% V5-gl = 14% where n = 10,563. The present records are obviously different from the previous ones in that crossing over in the V5-gl region is markedly reduced. While all the recessives were somewhat deficient, this in itself probably does not account for the reduced crossing over. Fraser (News Letter 1940) indicated that he was investigating the reason for marked differences in the complementary crossover classes in the in-V5 region. A study of the lineage of all these cultures may perhaps clarify the present results.
|Table 2.||+ + +/v5 ra gl|
|832 478||40 39||8 314||29 0|
Recombination percentages: v5-ra 6.2, ra-gl 20.2
Ratios: 909+ : 831 v5, 879+ : 861 ra, 1214+ : 526 gl
Fraser (News Letter 1941 p. 19) reported crossover percentages as follows: v5-ra 7, ra-gl 6, gl-ij 18. The present records agree for the first region but not for the second. However, the ratio of glossies to non-glossies is roughly 1:2.
|Table 3.||+ + +/ra gl ij|
|340 184||16 47||101 63||3 94|
Recombination percentages: ra-gl 18.9, gl-ij 30.8,
Ratios: 460+ : 388 ra, 582+ : 266 gl, 453+ : 395 ij.
The region ra-gl was also studied in another culture where 20.2 percent of crossing over was obtained. These two sets of data agree in fixing the length of this region at about 18-20 units. However, this is in contrast to the result of 6 units obtained by Fraser (News Letter 1941). The region gl-ij is longer (30.8) than in the previously reported data 18 (Fraser News Letter p. 19)
No final interpretation of these data will be attempted until I have had an opportunity to study the origin of all cultures. Even then, further work will probably be necessary.
M. J. Murray