SelfIncompatibility

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Self-Incompatibility

• S-alleles

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Gametophytic Incompatibility
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• It is believed that S-RNase acts to degrade RNA
  of self-pollen tubes, resulting in inhibition of
  self-pollen tube growth.

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(No Transcript)
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Sporophytic Incompatibility

• A pistil-specific S Receptor Kinase (SRK) at the
  surface of the pistil is responsible for the
  recognition of the incompatible pollen. The
  pollen has a Cysteine-Rich protein (SCR) that
  encodes a soluble, secreted ligand for the same
  receptor.

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Comparison
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Possible Cause of difference
Sporophytic
Gametophytic
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• The results of self and outcross pollinations of
  different aged flowers where the oldest flowers
  were at the left of each infloresence and the
  youngest at the right.  Older flowers are more
  self-compatible than younger flowers.

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Isolating Mechanisms

• Breeding failure between species

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Spatial

• Gene exchange reduced by distance alone
• Example Larches of the world

Siberian Larch
Western larch
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Ecological

• Usually associated with spatial
• Requirements are different thus keeping the
  species in different locations

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Reproductive

• Premating
• Mechanical

Aquilegia formosa
Aquilegia chrysantha
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• Ethological

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• Seasonal
• Length of life cycle
• Length of flowering season
• May vary from year to year
• Reduction in zygote formation
• Pollen may not germinate or tube may die after
  germination
• Pollen tube competition
• Biochemical antagonism may stop fusion of egg and
  sperm

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• Postmating mechanisms
• Reduction of hybrid survival
• Reduction of gene flow through hybrids
  (sterility)