Where do gametes originate

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Where do gametes originate?
Primordial Germ Cells (PGC) cells give rise to
eggs and sperm are set aside very early in
development Gametes (eggs and sperms) mature in
the gonads (ovary and testis)
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Influence of Sry on gonad development
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Nuclear transplantation
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Dolly her surrogate mother
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• egg jelly present in non-mammalian eggs
• glycoprotein meshwork
• frog jelly
• chick albumin/shell
• insect chorion

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Structure of an egg

• Vitelline envelope egg coat
• surround the egg plasma membrane
• glycoprotein extracellular matrix
• sperm receptor (galactosyl transferase)
• protect from mechanical damage
• specie-specific barrier to sperm sea urchin
  vitelline layer,
• mammalian eggs zona pellucida

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Mammalian egg
Plasma membrane
Zona Pellucida
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Plasma membraneregulate the flow of certain ions
Fuse with sperm membrane
Cortical Granules Different from yolk granules.
Membrane bound structuresSimilar to acrosomal
vesicles of the sperm Golgi-derived
organelle Contain proteolytic enzymes
Cortex Structures present immediately beneath
the plasma membrane
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Oogenesis
PGCs migrate to the forming gonad gt become
oogonia gt divide (mitosis) to become primary
oocytes
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• Cells arrest at prophase of meiosis I (G2
  equivalent phase)
• Primary oocytes grow Synthesis of cortical
  granules, accumulation of mRNAs/
• proteins.
• Oocyte maturation after hormonal stimulation
• Progress to meiosis I division give rise a
  secondary oocyte and a first polar body (2n)