title: rDNA site number polymorphism and NOR inactivation in natural populations of Allium schoenoprasum.
abstract: Nucleolar-organiser activity has been studied by silver staining and by in situ hybridization with an rDNA probe in two populations of Allium schoenoprasum. One population is monomorphic with NORs and rDNA sites terminal on the short arm of pair 8 in all individuals. The other populations is monomorphic for pair 8 NORs but is also polymorphic for NORs on the long arm of pair 7. All plants in this population carry ribosomal cistrons on both chromosomes of pair 7 but 0, 1 or 2 of these sites can be active in rRNA synthesis. Cis-acting nucleolar-suppression affects the pair 7 locus. We suggest that there has been progressive reduction in the number of NORs during the evolution of A. schoenoprasum.
authors.affiliation: Departamento de Genetica, Facultad de Ciencias, Universidad de Granada, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Garrido
authors.forename: M
authors.initials: M
authors.lastname: Jamilena
authors.forename: R
authors.initials: R
authors.lastname: Lozano
authors.forename: C
authors.initials: C
authors.lastname: Ruiz Rejon
authors.forename: M
authors.initials: M
authors.lastname: Ruiz Rejon
authors.forename: J S
authors.initials: JS
authors.lastname: Parker
mesh_terms: D000490:Allium / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D004739:England; D017403:In Situ Hybridization; D009697:Nucleolus Organizer Region; D011110:Polymorphism, Genetic; D016622:Silver Staining
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal