Development

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Development
Axolotl
Chicken
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Gametogenesis

• The formation of gametes occurs within the
  gonads (ovaries and testes.)
• Spermatogonia and oogonia undergo mitosis to
  produce primary spermatocytes and oocytes.
• Primary gametocytes undergo meiosis twice to
  produce four spermatozoa or a single ovum.

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Fertilization
The haploid egg and haploid sperm unite resulting
in a diploid zygote.
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Cell Cleavage

• Rapid divisions increase cell numbers with no
  increase in size
• 1st Cleavage 2 cells
• 2nd Cleavage 4 cells
• 3rd Cleavage 8 cells
• 4th Cleavage 16 cells
• 5th Cleavage 32 cells (morula)
• Hollow ball of cells (blastula) forms with a
  fluid filled cavity in the center (blastocoel)

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Gastrulation

• Invagination (denting inward) and involution
  (rolling inward) of cells producing blastopore.
• The 3 primary germ layers are established
• Ectoderm
• Mesoderm
• Endoderm

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Gastrulation in Aquatic Vertebrates

• Ectoderm formed as cells from the animal pole
  surround larger yolk cells which form the
  endoderm.
• Mesoderm formed at an involuting dorsal lip at
  the blastopore (see models)

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Gastrulation in reptiles, birds, and mammals

• The cells of the blastodisc which are adjacent
  to the yolk become endoderm.
• Mesoderm is formed at the involuting primitive
  streak (an elongated blastopore) on the dorsal
  surface of the blastodisc.

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Germ Layer Development

• Ectoderm
• Nervous system, cornea and lens of eye, epidermis
  of skin, epithelial lining of mouth and rectum
• Mesoderm
• Circulatory system, segmented muscles, skeleton,
  kidney, gonads, outer covering of internal
  organs, lining of thoracic and abdominal cavities
• Endoderm
• Pharynx, liver, pancreas, lining of digestive
  tract, lining of respiratory tract

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Axolotl Development
Early Gastrula
Cleavage (2 cells)
Cleavage (4 cells)
Blastula
Late Gastrula
Early Neurula
Early Tail Bud
Late Tail Bud
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Chick Embryo Development

• 4 day embryo removed from the egg
• http//www.youtube.com/watch?vBzvpa1SaGgY
• 9 day embryo inside egg
• http//www.youtube.com/watch?vTjeq58oLdVk
• Fertilized egg to a baby chick
• http//www.youtube.com/watch?vkwGkkOeoLTgfeature
  related

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Candling Interpreting what you see
Freshly laid egg (air pocket and yolk are
visible) if it is over a week old it is not
fertile
Fertile egg at approximately 5 days old. Notice
the faint blood vessels.
This egg is opaque, but it has a large,
off-center air pocket. It could contain a
dead-in-shell chick, or it could be an old rotten
egg.
Opaque egg the chick has developed to the point
that you cant see through the egg at all.
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Chicken Egg Candling

• Unfertilized Chicken Egg

• Fertilized Chicken Egg

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Todays Tasks

• Station 1 Model amphibian development
• Sketch 1 stage label layers other
  identifiable structures
• Station 2 Preserved and live frog embryos
• 1 sketch any stage
• Label developmental stage and identifiable
  structures
• Discuss questions in your discussion
• Station 3-4 Live axolotl, frog killifish
  embryos
• 2 sketches of axolotls at different developmental
  stages
• 2 sketches of killifish at different
  developmental stages
• Label developmental stages, and any of the
  following you can find yolk, head, tail, dorsal/
  ventral sides, eyes, blood vessels, heart
• Discuss questions in your discussion
• Station 5 Chick Embryos
• 2 sketches at different developmental stages
• Refer to description card to label all
  identifiable parts
• Discuss questions in your discussion