Polyploidy

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Polyploidy

• Polyploidy, Allopolyploidy, Autopolyploidy,
  Amphiploidy

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Definitions

• Polyploidy when an organism contains 3 or more
• times the haploid (1N) number of chromosomes.
• E.g. Normal for 2N (homologous pairs),
  polyploidy 3N or more)
• (Rare in ANIMALS, but common in PLANTS).
• Hermaphrodite animals usually are polyploidy,
  such as flatworms, and earthworms. Polyploid
  humans usually abort spontaneously.

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Human Polyploid Karyotype

• Usually they spontaneously
• abort however this one made it
• to full term!
• Polyploid triploid (3N)
• One parent contributes the
• normal 22 autosomes
• one sex chromosome, the
• other parent contributes
• the full 46 chromosomes.
• About 2 of conceptions! BUT
• could be more, as most abort.

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Definitions cont

• Allopolyploidy type of polyploidy, results
• from mating between TWO different SPECIES.
• THINK PLANTS!!!
• Species A mates with Species B to produce
  infertile hybrid. Failure during Meiosis
  (non-disjunction) doubles the number of
  chromosomes in they hybrid. The hybrid self
  fertilises to produce a fertile new species.
• AA BB AB (infertile hybrid)
• AB non-disjunction AABB, gametes AB (pollen),
  AB (egg)
• Self fertilise AB AB AABB (fertile new
  species)

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Definitions cont

• Amphiploidy The name given to the step when
  there is an
• error in meiosis (non disjunction) resulting in
  double the
• number of chromosomes in the hybrid.
• In plant evolution especially wheat this has
  happened and with more than two species
  interacting to form a fertile new species.
• AA mates with BB AB (infertile hybrid)
• Amphiploidy results AABB (new fertile species)
• AABB mates with DD ABD (infertile hybrid)
• Amphiploidy results AABBDD (new fertile species
  with all the desirable traits)

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Allopolyploidy - wheat
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Definitions cont

• Autopolyploidy form of polyploidy, results from
• mating between SAME SPECIES.
• E.g. Chromosomes fail to separate during
  meiosis. Species A mates with species A,
  non-disjunction occurs in both individuals or
  within one plant resulting in their gametes
  carrying AA or nothing. When AA AA fertilise
  (or self fertilise) AAAA (fertile hybrid).
• If non-disjunction occurs in only one individual
  then the hybrid will be infertile. AA A AAA
  (infertile)

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Autopolyploidy
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Summary

• Non-disjunction this is the process that leads
  to these mutations and how species can go from
  producing infertile hybrids to fertile new
  species!
• Colchicine drug used to double chromosome
  number. Destroys spindle fibers so chromatids
  cant separate.
• BUT why are hybrids usually infertile?

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WHY?

• All species have their specific number of
• chromosomes (plant 6CH, 3 homologous pairs),
• during meiosis the pairs have to match up before
• they separate.
• Scenario
• Non-disjunction occurs in female part (Egg).
• One of her eggs containing 6 CH is fertilised by
  a pollen that has gone through meiosis without
  error (pollen 3 CH).
• Seed 9 CH.
• The seed germinates and becomes a plant that is
  infertile because when its reproductive
  structures go through meiosis they cant pair up
  as there is not an even number of CH (half of 9
  4.5). However if you can double the number of CH
  (9x2 18) amphiploidy, you can get gametes
  (pollen and eggs) carrying CH that can pair up
  evenly.
• Results in a new species! remember this for
  speciation (evolution)