TY  - JA
AU  - McWhirter,K.S.
AU  - Brink,R.A.
TI  - Continuous variation in level of paramutation at the R locus in maize
SN  - 0016-6731
PY  - 1962///
CY  - Baltimore (USA)
PB  - Genetics Society of America
KW  - Genes
KW  - AGROVOC
KW  - Loci
KW  - Alleles
KW  - Mutagenicity
KW  - Mutation
KW  - Maize
N1  - Peer review
N2  - Eighty-three Rsc mutants (self-colored aleurone, green seedling) from the strongly paramutagenic Rst allele (stippled aleurone, green seedling) were characterized for paramutagenic action by testcrossing the respective RrRsc heterozygotes (all containing standard Rr: colored aleurone, red seedling) on rgrg females (colorless aleurone, green seedling). The Rsc mutants were found to vary continuously in level of paramutagenic action from high levels not significantly different from that of the parent Rst factor (strongly paramutagenic) to no detectable effect on the pigment-producing action of Rr (nonparamutagenic) . There were 16 mutants of the latter class, and 36 of the former. Each of the remaining 31 Rsc alleles was paramutagenically active at one or another intermediate level. The level of paramutation for a given RrRsc combination was highly reproducible, and was not altered when the Rsc allele was maintained in heterozygous condition by successive backcrosses to RrRr or Rg5 rr plants. The results show that the aleurone pigment-producing potential of standard Rr may be reduced to any one of a graded series of levels, each of which is then gametically transmissible. The pigment-producing potential of Rr is reduced in two steps when the allele is first passed through a heterozygote carrying a weakly paramutagenic Rsc mutant and then through a heterozygote with the strongly active Rst factor. The occasional occurrence on single ears from RstRst x rrrr matings of two or more independent self-colored mutants from stippled that are subsequently found to differ significantly in level of paramutagenic action suggests that change in aleurone pigmentation and paramutagenicity are coincident events. Crossing-over in the vicinity of the R locus as the basis of the coincident changes was excluded. The simultaneous alteration in aleurone pigmentation and paramutagenicity in mutation of Rst to Rsc may be formally interpreted in terms of transposition of an assumed component of the stippled allele that inhibits aleurone color when in one position and paramutagenic action in variable degree when at one or another particular site nearby. An attempt to verify this hypothesis by screening more than a million gametes from RscRsc plants for back mutations to stippled (i.e., transpositions of the assumed inhibitor from its new site back to old position) gave a negative result. Seventeen mutations of Rsc were observed, but none conditioned the stippled phenotype.
UR  - https://www.genetics.org/content/47/8/1053.article-info
T2  - Genetics
ER  -