Mapping the narrow sheath duplicate factor pair
--Mike Scanlon and Michael Freeling

The narrow leaf and plant stature mutant narrow sheath (ns) was identified by Elsing and Albertsen as a single factor trait which sometimes displayed non-Mendelian patterns of inheritance (MNL 66:49-50, 1992). Subsequent analyses have determined that, in the original inbred line in which the mutant was isolated, the ns phenotype is inherited as a single recessive factor trait (Table 1). However, in the inbred lines Mo17 and B73, and in our laboratory Mutator-active inbred stock, the ns trait displays duplicate factor inheritance (Table 2). In order to locate the ns duplicate factor pair to chromosome arm using the B-A translocation series (Kindiger and Beckett, MNL 60:43, 1986), plants heterozygous for each of the dual factors were crossed as female onto hyperploid heterozygotes. Hypoploid plants were selected among the F1 progeny on the basis of 50% pollen semi-sterility, and plant phenotype (where applicable). The F1 hypoploids were either self-pollinated or backcrossed to ns mutants. The ratios of ns vs. non-mutant seedlings scored in the progeny of these crosses are presented in Table 3. The data indicate that the ns duplicate factors are located on chromosome arms 3S (ns1) and 4L (ns2). Molecular markers are now being used to RFLP map the ns loci to more precise locations.

Table 1. Number of progeny obtained from self of normal plants generated from ns x ns / + cross in original stock obtained from Pioneer Hi-Bred International.
 
Self # Mutant No. Normal No. Total No. Mutants (%)
1 24 62 86 27.9
2 14 40 54 25.9
3 7 29 36 19.4
4 48 150 198 24.2
5 8 25 33 24.2
6 12 21 33 36.4
7 22 78 100 22.2
Sum total 135 406 541 24.9
Fits a 3:1 ratio

Table 2. Combined sum total of number of progeny obtained from selfs of ns/Mo17 and ns/B73 plants.
 
F1 genotype  Mutant Normal  Total  Mutants (%)
ns/Mo17  66 849 915 7.21
ns/B73 68 1153 1221 5.57
Combined sum total 134 2002 2136 6.27
X2 = 0.001 Fits a 15:1 ratio

Table 3. Summary of ns1 and ns2 TB mapping results
 
TB parent Hypoploid F1 plants (#)* F1 cross Total ns progeny (#) Total progeny (#) ns progeny (%)
1S 3 ns backcross 8 28 28.5
1L 2 ns backcross 26 111 23.4
3S 6 ns backcross 93 210 45.7
3L 8 ns backcross 97 410 23.7
4S 2 self 7 114 6.14
4S 2 ns backcross 13 81 16.3
4L 3 ns backcross 52 105 49.5
5S 9 ns backcross 93 409 22.7
5L 3 ns backcross 33 154 21.4
6S 2 ns backcross 13 70 18.5
6L 6 ns backcross 59 275 21.5
7S 3 ns backcross 35 157 22.3
7L 7 ns backcross 55 227 24.2
8L 3 ns backcross 38 174 21.8
9S 2 self 6 100 6.0
9S 5 ns backcross 29 146 19.9
9L 1 ns backcross 6 30 20.0
10S 3 ns backcross 35 160 21.9
10L 4 ns backcross 52 249 20.9
* only hypoploids which segregated ns mutant progeny included in table


Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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