hcf*19: linkage with ys3 and d; allelism of hcf*-19A and hcf*-19B

Allelism: Two distinct lethal photosystem II lesions were isolated from a single M2 progeny of Neuffer's nuclear mutant collection (Leto and Miles, MGNL 53: 38, 1979). One of these, hcf*-19A (previously designated hcf*-19g), was found to be missing a 32 kD thylakoid protein and had no observable PSII electron transport activity. The second, hcf*-19B (previously hcf*-19yg), contained the 32 kD protein absent from hcf*-19A and had partial (20-40% of normal) PSII activity. The pollen of three individuals potentially heterozygous for hcf*-19B was used to fertilize several plants potentially heterozygous for hcf*-19A. Since the parents in both cases were derived from ears of selfed heterozygotes for the respective mutations, 2/3 of the viable parent plants should be +/hcf for the hcf locus in question. Of eleven such crosses, the progeny of nine segregated approximately one-fourth hcf seedling-lethals. Therefore, hcf*-19A is allelic to hcf*-19B.

The original designations yg or g for the different hcf*-19 phenotypes have been dropped because they do not always correspond to a given phenotype. In F2 progeny from crosses of +/hcf*-19 with the inbred Mo17 or with a hybrid of inbreds Mo17 and N28 (the latter F2 progeny was kindly supplied by M. G. Neuffer), both hcf*-19 phenotypes (confirmed by gel electrophoresis) were either fully green or very slightly pale green.

Linkage: F2 progenies of a cross between d/d, ys3/ys3, +/+ and +/+, +/+, +/hcf*-19A were analyzed. Recombination values were calculated using the tables of Fisher and Balmukand (J. Gen. 20:79, 1928):

Table.

The total number of individuals observed was 723. Data for 5 separate F2 progenies are combined in the table. The distributions of phenotypes were approximately equivalent for different progenies. To facilitate scoring, the hcf phenotype was equated with lethality (over 100 lethal seedlings were initially identified as hcf). Of the 15 ys3 hcf*-19 recombinants, 9 were also d.

The ys3 locus has been assigned to the long arm of chromosome 3 by analysis of crosses with B-A translocations (Beckett, MGNL 49:131, 1975) and appears to be near the centromere (Wright, MGNL 35:111, 1961). The hcf*-19B allele is uncovered by TB-3Sb (Leto & Miles, MGNL 51:58, 1977), placing this locus on the short arm of chromosome 3. Thus, the high recombination frequency observed here between d and hcf*-19A is difficult to explain. If one ignores the linkage data for d and hcf*-19, the gene order would be: d hcf19 ys3. If the assignment of hcf*-19 to the short arm of chromosome 3 is ignored, the gene order would be: d ys3 hcf*-19. A cross of cr/cr, d/d, Lg3/+ or Lg3 with +/+, +/+, +/hcf*-19 has been performed and the F2 progeny should be available for screening in late spring 1982. Crosses of hcf*-19A and hcf*-19B with TB-3Sb and TB-3La will be performed this spring in the greenhouse.

Mary Polacco and M. G. Neuffer


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