Transpositions of Modulator in Maize into Divided and Undivided Chromosome Segments

Abstract

VARIEGATED pericarp , a highly unstable allele in maize, comprises two distinct and separable components, symbolized as P^rr and Mp. The P^rr gene which, when unaccompanied locally by Mp, conditions uniformly pigmented (self-coloured) pericarp and cob is fixed in position at the P locus in the short arm of chromosome 1. In contrast, modulator (Mp) is an element which is transposable independently in somatic cells from this position to a wide variety of other chromosome sites, and preferentially to those nearby. Mp, when immediately associated at the P locus with P^rr, suppresses pigment-producing action of the latter, giving colourless pericarp and cob. The composite, variegatod pericarp phenotype is the outcome of numerous Mp transpositions during ear development, resulting in P^rr expression in the form of irregularly distributed coloured pericarp sectors of various sizes on a colourless background^1,2.