We would like to report our preliminary results on the use of compound B-A translocations to localize genes on the long arm of chromosome 5. We are working with ethylmethane sulfonate (EMS)-induced mutants generated by Dr. M. G. Neuffer, who provided us with M2 populations segregating for the various mutants. He utilized TB-5La to place these mutants to the long arm of chromosome 5. To avoid confusion, we will use his allele designations and E numbers. This report will be limited to seedling mutants.
The accompanying table gives a short description of the mutant phenotypes as we see them, allelism, and approximate map locations on the long arm of chromosome 5. We have generated a series of compound B-A translocations involving the long arm of chromosome 5 as described in Shadley and Weber (MNL 55:124, 1981). The compound B-A translocations were derived by crossing TB-5La-containing plants with specific reciprocal translocations which have one of their breakpoints in the long arm of chromosome 5 distal to the breakpoint of TB-5La. Embryos hypoploid for the compound B-A translocations are hypoploid for the segment between the breakpoints, and are not hypoploid for the segment distal to the breakpoint. By utilizing compound B-A translocations with different breakpoints, it is possible to generate plants hypoploid for different portions of the long arm of chromosome 5. We believe that this approach has great merit and could be used in maize to generate segmental aneuploids in much the same way as is being done in Drosophila melanogaster by Lindsley et al. (Genetics 71:157, 1972). Specifically, we have generated and are using the following B-A translocations with the following breakpoints: 1) TB-5La-3L5521 with breakpoints at 0.1 and 0.48, 2) TB-5La-3Lb with breakpoints at 0.1 and 0.57, and 3) TB-5La-3L7043 with breakpoints at 0.1 and 0.61.
All four pale-green mutants (pg*-296, pg*-408 pgv*-71. and pgv*-735) were found to be allelic, however, some of the other families supplied by Neuffer also segregated for pale-green seedlings. For example, the line containing wl*-1308 (wl gr lf tp) segregated for pale-green seedlings, and when these were allele-tested with pg*-735 and pg*-71 some of the progeny segregated for pale-green seedlings. For this reason, we believe that it is possible that one of the mutagenized lines contained a pale-green mutant, and the four pale-green mutants may not necessarily each represent independent mutations of this locus. Also, two ears from an allele test between wl*-1308 and wl*-199 (gr wl) segregated for a phenotype similar to that found in the 1308 parent. Because of the limited number of positives from this cross, we are not sure of the allelic relationship between these two mutants, and we cannot preclude a mixup of the mutant families.
A pg*-408/pg*-71, Pr/Pr X Pg/Pg, pr/pr cross was made in 1982, and the F1 generation was selfed in 1983. Analysis of eight ears suggests a map distance of approximately 50 map units between these two loci; thus, the pale-green locus could be near the yg1 locus. Chang (MNL 56:44) reported that pg*-735 is allelic to wlv*-473; thus, these five mutants are apparently allelic, and possibly allelic to yg. Obviously, these allele tests need to be made. Because of their approximate chromosome locations, allele tests between w21 and w22 with v3 and v21 should be done, as well as allele tests between wl*-199, wlv*-308, w*-sect206, and v2.
Three mutants, nec*-409, nec*-493 (tan necrotics) and gl*-681 were not uncovered by TB-5La; however, they were uncovered by compound TB-1La-5S. Thus, these three mutants are on the short arm of chromosome 5. Allele tests between the two tan necrotic mutants produced two types of mutant plants, those which developed necrotic bands early and die as young seedlings and those which develop necrotic bands later and survive to maturity. Crosses can be made with these latter types. Glossy seedlings from gl*-681 are smaller in size than their normal sibs. No allele tests have been made between the gl*-681 and tan necrotic mutants.
J. D. Shadley and D. F. Weber
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