RECONSTITUTION OF THE Rr COMPOUND ALLELE IN MAIZE

[摘要] The Rr :standard allele in maize, which conditions anthocyanin pigmentation in plant and seed tissues in the presence of appropriate complementary factors, is associated with a tandem duplication. The proximal member of the duplication carries P , the plant pigmenting determiner and the distal member member carries S , the seed pigmenting determiner. Derivatives from Rr that have lost S function are designated rr . They represent either losses of the distal member of the duplication ( P derivatives) or mutations of S to s ( P s ). Derivatives that have lost P function are designated Rg , and represent either losses of the proximal member of the duplication ( S derivatives) or mutations of P to p ( p S ).—All four possible types of rr/Rg heterozygotes were tested for their capacity to yield Rr reconstitution by crossing over. No Rr derivatives were obtained from P/S heterozygotes, a result consistent with the view that P and S occupy corresponding positions in homologous chromosome segments. Rr reconstitution was detected in both tandem duplication heterozygotes P s/S and P/p S , and was found to be about ten times more frequent in the latter. The ratio of Rr reconstitution in the two heterozygotes is a function of position of the anthocyanin marker within the duplicated segment. The data from these heterozygotes allow one to measure the distance between P and S , that is to say, the genetic length of the duplicated segment. This distance was found to be 0.16 map units. The highest frequency of Rr reconstitution was obtained from P s/p S heterozygotes, since direct pairing (see PDF) as well as the p//s type of displaced pairing have the potential to produce Rr derivatives. One of the Rg derivatives used in this study, Rg6 , was found to back-mutate in some sublines to Rr . The basis for this instability remains unknown.

[学科分类] 医学（综合）