A Genetic Change Associated with the R Locus in Maize Which Is Directed and Potentially Reversible.

NTEGRITY of the gene in heterozygotes, first inferred from MENDEL'S (1865) I Pisum data and repeatedly corhrmed since in a wide variety of organisms, is regarded as a universal principle in Mendelian heredity. Departures from the law have been reported from time to time, only to prove unfounded, in most instances a t least, on close analysis. The present study is concerned with a seeming exception to the rule a t the well-known R locus in maize conditioning aleurone and plant color. All the RI c? gametes (self-colored aleurone) produced by RrRSt plants (heterozygous stippled aleurone) were found to give a different phenotype in testcrosses on rrrr 9 9 (colorless aleurone) than the R' 8 gametes formed by R'R' sibs. The altered form of R' in the Rrrr testcross progeny is transmitted through the succeeding sporophyte generation and, therefore, is heritable. The change in Rr is potentially reversible with equal regularity. R' gametes formed by all RrRI plants derived from RrRst heterozygotes by seliing were found to have regained the standard (or near-standard) level of pigment-producing action in testcrosses with rrrr 9 9 . The present communication is a preliminary account of this unusual phenomenon.