Animal Development Fertilization, Cleavage, Gastrulation

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Animal DevelopmentFertilization, Cleavage,
Gastrulation

• Mrs. Oldendorf
• AP Biology

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Frog development
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Fertilization
Haploid Haploid ? Diploid
The sperm Note the acrosome and the nucleus and
location of mitochondria
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The Acrosomal Reaction Sea Urchins (external
development)

• upon contact with eggs jelly coat, sperms
  acrosome is released
• enzymes make hole in the jelly coat
• fusion of egg and sperm membranes triggers
  depolarization of the membrane (fast block to
  polyspermy)
• cortical granules fuse with plasma membrane, clip
  off sperm binding receptors (slow block to
  polyspermy)

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In Mammals (internal fertilization)

• sperm need the environment of the female tract to
  be able to fertilize (capacitation 6 hrs)
• follicle cells surround the ova (egg) called
  the zona pellucia have receptors for sperm that
  induces an acrosomal reaction
• no fast block system in mammals, only slow block

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Development (cleavage and gastrulation)
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Terms

• Cleavage stages of early development (cell
  divisions)
• Blastula 1st 5 7 cleavages ? hollow ball of
  cells surrounded by blastocoel
• Blastocoel fluid filled cavity that is the
  future body cavity (animal hemisphere)
• Vegetal pole where yolk (stored nutrients) is
  concentrated
• Animal pole the opposite pole of where the yolk
  is

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More terms

• Archenteron future gut (digestive system)
• Blastopore future anus
• Germ layers (3) ectoderm, endoderm, mesoderm
• Gastrula a 2 or 3 layered embryo

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The EGG

• The upper hemisphere of the egg the animal
  pole is dark.
• The lower hemisphere the vegetal pole is
  light.

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Holoblastic Cleavage

• In eggs that contain no or only moderate amounts
  of yolk, cytokinesis divides the cells
  completely.
• - (like frogs and mammals)

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Meroblastic Cleavage

• In eggs that contain a large amount of yolk,
  cytokinesis does not divide the egg completely.
• - also found in the eggs of fish, reptiles, and 4
  species of mammals the monotremes

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Cleavage

• Series of mitoses in zygotic nucleus

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First cleavage

• A furrow appears that runs longitudinally through
  the poles of the egg
• This divides the egg into two halves forming the
  2-cell stage

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As cleavage continues

• the cells in the animal pole begin dividing more
  rapidly than those in the vegetal pole (and thus
  become smaller and more numerous.)
• By the next day, a hollow ball of thousands of
  cells called the blastula has been produced.
• A fluid-filled cavity, the blastocoel, forms
  within it.

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During this entire process

• There has been no growth of the embryo
• Not until the blastula gt 4000 cells is there any
  transcription of zygote genes
• (up until now the activities have been run by
  gene products mRNA and proteins from the mother)

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Gastrulation

• The invagination (pushing inward) of cells in the
  region of the embryo once occupied by they grey
  crescent
• This produces
• An opening (blastopore) that will be the anus
• A cluster of cells that becomes Spemann Organizer

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3 Germ Layers are formed

• Ectoderm
• Mesoderm
• Endoderm

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Spemann Organizer will.

• Develop into the notochord (precursor to
  backbone)
• Induce ectoderm to form neural tissue
• Neural fold stage ? then forms the neural tube ?
  develops into brain and spinal cord
• FOLIC ACID!!!

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Differentiation

• Cells of the embryo take on specific functions
• Neurons, blood cells, muscle cells, epithelial
  cells, etc etc etc

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Genetic Regulation of Cell Differentiation

• Control Factors in cytoplasm of egg
• Evidence remove nucleus from fertilized egg and
  cleavage still occurs
• Egg has maternal mRNA in unfertilized egg ?
  proteins direct change

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• Events of Fertilization
• Point where sperm enters determines location of
  grey crescent (across from) determines dorsal
  axis (nervous system)

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• Role of Nucleus
• All cells of embryo have same set of chromosomes

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Morphagenesis

• Formation of overall body pattern
• Driven by chemical concentration gradients set up
  by morphogens (signaling molecules) that diffuse
  through the tissues of an embryo during early
  development, concentration gradients

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• involves homeobox genes or homeotic gene
• Arranged in a definite order and determine the
  anterior and posterior ends of body