In last year's MNL (MNL72:79), we reported the results of a 3-point linkage test for su1, bm3, and gl7 on 4S. This data indicated that the correct order of the genes on chromosome 4 is su1-bm3-gl7 (this is the local order--the global order can not be determined until the global order of su1 and bm3 are known). Since both su1 and gl7 are uncovered by TB-4Sa, it follows that bm3, which is located between these two loci, should also be uncovered by TB-4Sa. However, the only previously published data about the chromosome location of bm3 (Beckett, JB, MNL 49:130-134, 1975) indicated that bm3 is not uncovered by TB-4Sa. Last winter, we repeated this test, crossing TB-4Sa onto two separate su1 bm3 stocks maintained by the Coop. This summer, we observed the progeny of these crosses, and noted that 18 out of 50 plants grown from these crosses had brown midribs. The TB-4Sa stock itself does not carry bm3. We conclude that bm3 is located distal to the 4S breakpoint of TB-4Sa.
 

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