Using a TB-8Lc stock supplied by Jack Beckett, reciprocal crosses were made with several Mdh1 and Idh1 tester stocks. For one such cross, both alleles at Mdh1 and both alleles at Idh1 could usually be scored unambiguously. The TB-8Lc parent carried Idh1-4 and Mdh1-6, while the tester stock carried Idh1-2 and Mdh1-1. Of 36 plants tested using the TB-8Lc plant as male, most were doubly heterozygous, Idh1-2/4, Mdh1-1/6. Not all plants could be scored with absolute certainty for Idh1, but several plants were Idh1-2, Mdh1-1/6, with no Idh1 allele contributed by the male parent. Since the latter plants were heterozygous for Acp1, Idh2, and Mdh2, as had been expected (the two putative parental plants were homozygous for different alleles for these three loci), contamination appears unlikely. (Sixteen other loci also revealed no contamination, but the latter were less informative.) Thus, it appears that Mdh1 lies outside the region spanned by TB-8Lc, while Idh1 lies within that region.

M. M. Goodman, C. W. Stuber and K. J. Newton

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