Rick, C. M.
The following unrelated tests are reported since they might be of interest in confirming previously suspected linkages and in assisting in placing loci on the maps.
Previous trisomic tests (TGC 10:37) indicated the presence of vg on chromosome 4 and of sd on 7. Linkage tests with markers on the respective chromosomes were facilitated by the use of combinations already available of e and mc in one stock and vg and sd in another. The segregation of 6 other genes in the F2 did not help much, but it was possible to work out the pertinent segregations in the field-grown F2. The indications of the trisomic tests were nicely confirmed by the vg-e and mc-ad linkages.
Recent progenies afforded an opportunity to test the sf-rv ocabination in coupling phase. It is interesting to note here that the frequency of sf is severely reduced presumably because coupling linkage forces it to do what rv does, whatever might be responsible for the reduced rv frequency. With such disturbed monogenic frequencies, the resultant estimates of linkage values are not very trustworthy--hence the discrepancy between the mean of 22.5 obtained for coupling phase and the previously reported 34.0 from repulsion.
In the process of synthesizing a multiple seedling marker stock for chromosome 2, a three-point test was obtained for aw-Me-wv. As revealed in the table below, the data are consistent with a locus of wv on the other side of Me from d\1. As the first seedling marker in this region, wv should prove useful.
Adjusted
Combination contingency Mean
m t Phase + + + t m + m t Chi-square Co. co.
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vg - e F2-R 201 77 91 3 23.56 21.0
mc - sd F2-R 189 92 88 3 29.81 19.0
af - rv F2-C 268 22 35 35 72.97 20.5 22.5
197 20 20 19 36.94 23.0
257 30 34 34 55.53 24.0
wv - aw F2-R 909 394 385 10 126.80 16.5
wv - Me F2-C 102 1201 358 37 1048.06 7.5
Me - aw F2-C 453 7 841 397 170.91 12.5
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The above linkage values, all derived from F2 data, suffer the same
shortcomings of such sources. They should be regarded only as rough
estimates, presently being of greater usefulness for detecting linkages and
determining order of loci than for precisely determining loci.