Definition: More than two sets of chromosomes per nucleus

• Triploid, tetraploid, pentaploid, hexaploid, etc.
• Range of chromosome numbers: 2n=4 - 500 (for flowering plants- dicots)
  • Haplopappus gracilis (2n=4)
  • Kalanchoe (2n=500)
  • Ophioglossum reticulatum (2n=1260)
• Effect of even vs. odd polypoidy
  • Even often fertile
  • Odd are sterile
• Polyploid series
  • Gossypium: 2n=26, 52 (i.e., n=13, 26)
  • Nicotiana tabacum group: 2n=24, 48 (n=12, 24)
  • Triticum: 2n=14, 28, 42 (n=17, 14, 21)
  • Rosa canina group: 2n=14, 28, 35, 42
  • Crepis occidentalis group: 2x, 3x, 4x, 5x, 7x, 8x
• Base number=lowest common denominator of haploid numbers
• Range of ploidy levels
  • Potentilla: 2n=14 to 2n=112 (16-ploid)
  • Chrysanthemum: up to 2n=198 (22-ploid)
  • Senecio roberti-friesii: 2n= ca 180 (36-ploid)
  • Poa litorosa: 2n= ca 265 (ca 38-ploid)

Frequency of polyploidy

• Varies across plant groups
  • Ferns: 95% of species
  • Flowering plants: 70% of species
  • Conifers: few

Types of Polyploidy

• Autopolyploid
  • Definition: duplication of sets of chromosomes involving only one species (e.g., genome = AAAA)
  • Occurrence: not common in nature, but frequent in cultivated plants
    • Triploids: banana, lime, seedless watermellon, lilies, azalea
    • Tetraploids: potato, coffee, peanut
    • Hexaploids: sweet potato, plum
  • Origin
    • Somatic doubling
    • Unreduced gametes
  • Evidence of Origin
    • Chromosome bahavior during meiosis
      • Multivalents
    • Genetic markers
    • Quantitative changes in morphology, not qualitative
• Allopolyploid
  • Definition: three or more sets of chromosomes, derived from two or more different species (e.g., genome = AABB)
  • Occurrence: very common
  • Origin
    • Hybridization followed by Unreduced gamete production
    • More frequent in self-compatible species
  • Evidence of Origin
    • Increased size of structures (characteristic of polyploids in general)
    • Morphologically intermediate (charactersitics of hybrids in general), but exceptions are known
    • Cytological evidence
      • Sets of chromosomes that differ in structure in same nucleus
      • Unusual meiotic figures
        • Univalent, trivalent or quadrivalent formation
    • Inverse relationship between fertility of diploid hybrids and tetraploid derivative, but chromsome pairing behavior is also subject to direct gennetic control, so this relatioonship is not always observed.
• Autoallopolyploid
  • Definition: contains duplicated sets from one species plus at least one set from a different species (e.g., AAAABB)

Polyploid Complexes

• Involves processes of
  • Related species with somewhat different genomes
  • Autopolyploidy
  • Hybridization
  • Autoallopolyploidy
• Asplenium fern example
• Clarkia
• Triticum-Aegilops