3. Chromosome 6 Linkage Studies.--A stock of ms pb has been established. The linkage of pb with Y is very close.

Classification for su2 has not been very satisfactory in material grown here at Minnesota. The data reported by me in the Coop Letter of March 23, 1937 (p. 15) indicated the order y-pl-su2, with about 8% recombination between su2 and Pl. It was noted there that the separation for Yy was poor. Since then Horovitz et al. (Anales Inst. Fitotecn. S. Catalina 3:37, 1941) reported a sux between Y and Pl. One backcross test with Pl using su2 as the female parent indicated 15% recombination, but all the recombinations were found in the non-sugary class. One test of su2 vs ms was set up as follows:

(ms +)
(+ su2)
was crossed on a ms Su2 Su2 stock and the progeny grown. The open pollinated ears were examined to determine the number of homozygous Su2 and heterozygous su2 in the normal and ms classes, from which the per cent recombination can be calculated. The method seems to be usable. In this case, 32.8% recombination was observed between ms and su2. These results are not satisfactory, however, since in the ms class there was 41.5% while in the non-ms class there was 45.4%. Intercrosses of su2 with Horovitz's sux have not been entirely satisfactory but they seem to indicate the two are the same.

Red glume collar in the tassel florets appears to show linkage with Pl in certain cultures, not in others.

A silky character is closely associated with antherless in the stock obtained from the Corn Coop. This silky vs Y showed 16.5% of recombination.

Trisomic tests for location of new factors in chromosome 6 : bas (barren stalk in a sweet corn), a new silky from a single cross, and a new stock of tinged (tn) show normal disomic ratios. The midget dwarf (mi) shows closer fit to a trisomic ratio than to disomic, although classification was not too certain.

C. R. Burnham

The following have assisted in the work at various periods: Gertrud Stanton, C. H. Li, T. J. Liang, and H. R. Highkin.