title: Permanent translocation heterozygosity in dioecious Baccharis coridifolia DC. (Asteraceae).
abstract: The karyotype of Baccharis coridifolia DC., a dioecious diploid species consists of 16 chromosomes with median (m) and 2 with submedian centromeric positions (sm) (2n = 18). Meiotic analyses of 219 male plants belonging to 12 populations showed across a wide geographical range one quadrivalent and seven bivalents in all of them. The quadrivalent involves the four biggest m chromosomes and probably constitutes a sex multivalent carrying in tight linkage the sex genes and provides a mechanism whereby permanent translocation heterozygosity is maintained. In metaphase I alternate orientation of the quadrivalent was predominant (85.71%). Fourteen megaspore mother cells were analyzed and did not show the quadrivalent. A model for the origin and maintenance of the sexual translocation system is presented. It is assumed that there are two non-allelic factors M and n; M would be a dominant female suppresor and n a recessive male-suppresor. The excess of male plants observed in several populations at different localities might result from heterotic effects of some gene complexes carried by the translocation. This excess probably ensures a good supply of pollen for the vagaries of insect pollination at flowering time.
authors.affiliation: Instituto de Botánica "Darwinion", San Isidro, Buenos Aires, Argentina. jhunziker@darwin.edu.ar
authors.forename: Juan Hector
authors.initials: JH
authors.lastname: Hunziker
authors.forename: Arturo Federico
authors.initials: AF
authors.lastname: Wulff
authors.forename: Alejandro
authors.initials: A
authors.lastname: Escobar
mesh_terms: D019659:Asteraceae / Q000235:genetics*; D032461:Chromosomes, Plant; D006579:Heterozygote; D014178:Translocation, Genetic