Permanent translocation heterozygosity and sex determination in East african mistletoes.

Viscum fischeri has 2n = 23 chromosomes in male plants. These fornm 7 bivalents and a translocation chain of 9 chromosomes during meiosis. Pollen with 11-and 12-chromosome genomes is thus produced. Female plants have 2n = 22 chromosomes and produce 11 bivalents during meiosis. Sex determination is technically a rare multiple X-multiple Y type, but more importantly it provides the mechanism whereby permanent translocation heterozygosity is maintained in the system. In a second species, Viscum engleri, male plants have 2n=28 chromosomes associating as 11 bivalents and a ring of 6 chomosomes at meiosis.