Translocation heterozygosity and sex ratio in Viscum fischeri

Summary Male plants of V. fischeri have 2n = 23 and constantly produce seven bivalents and a multivalent chain of nine chromosomes at meiosis. Regular assortment results in transmission of 11- and 12-chromosome genomes via the pollen. Female plants have the chromosome number 2n = 22 and are homozygous for the 11-chromosome genome. The multivalent chain in the males is a consequence of reciprocal translocations, one of which was Robertsonian and one of which involved the chromosome carrying the sex determination factors. There is a constant female-predominant sex ratio of approximately 1:2 in V. fischeri , possibly maintained by gamete selection; the genes involved may have been linked with the sex determination mechanism through the translocation system.