Canina Meiosis
The dog roses, the Canina section of the genus Rosa (20-30 species and subspecies, which occur mostly in Northern and Central Europe), have an unusual kind of meiosis that is sometimes called "permanent odd polyploidy" although it can occur with even polyploidy (e.g. in tetraploids or hexaploids). Regardless of ploidy level, only seven bivalents are formed leaving the other chromosomes as univalents. Univalents are included in egg cells, but not in pollen. Dogroses are most commonly pentaploid, i.e. five times the base number of seven chromosomes for the genus Rosa, but may be tetraploid or hexaploid as well.
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