Last year we reported (MGCNL 53) that a mutant (hcf*-26) blocked in light reaction photosynthesis was beyond the middle chromomere of the satellite and could be located in the distal chromomere. The mutant hcf*-26 possesses a yellow-green phenotype and had been reported to be uncovered by TB-6Sa (Leto and Miles, MGCNL 51:57-59). In order to more precisely cytogenetically locate hcf*-26, we crossed heterozygous satellite-interchanges as the female parent with heterozygous hcf*-26 plants as male parent. Under our greenhouse sandbench conditions, seed from self-pollinations of the heterozygous hcf*-26 plants resulted in green and near-luteus seedlings. None of the crosses between the heterozygous interchanges as female and heterozygous hcf*-26 as male yielded near-luteus seedlings when the satellite breakpoint was distal to the breakpoint of interchange T4-6(5227), which is located between the middle and distal chromomeres. Our results indicate that hcf*-26 is located between the breakpoint of T4-6(5227) and the proximal end of the distal chromomere marked by T3-6b. Thus, hcf*-26 is either between the middle and distal chromomeres or in the proximal portion of the distal chromomere. The breakpoint of T5-6(8219) has not been localized cytologically within the satellite; the lack of near-luteus seedlings in testcrosses of heterozygous T5-6(8219) and heterozygous hcf*-26 plants suggests that the breakpoint is in the distal chromomere.
Table 1. Tests to cytogenetically locate hcf-26. Smaller seed and a
portion of remaining seed from crosses of heterozygous interchanges as
female parent with heterozygous hcf-26 plants were planted. Data were collected
from seed produced during the summers of 1978 and 1979.
| Smaller seed2 | Remnant seed | |||||
| Interchange | Satellite1 break pt. | Number of crosses | Green | Chlorophyll deficient | Green | Chlorophyll deficient |
| 3-6b | proximal end of distal chromomere | 4 | 144 | 0 | 259 | 0 |
| 2-6(001-15) | distal end of distal chromomere | 3 | 162 | 0 | 273 | 0 |
| 6-7(7036) | distal end of distal chromomere | 6 | 115 | 0 | 325 | 0 |
| 5-6(8219) | "satellite" | 2 | 34 | 0 | 70 | 0 |
1The satellite is comprised of 3 chromomeres in these strains.
2Smaller seeds are expected to include Dp-Df heterozygotes.
R. L. Phillips and S. A. Thompson
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