ANIMAL EMBRYOLOGY

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ANIMAL EMBRYOLOGY

• BIOLOGY II
• CDEHS

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FERTILIZATION AND EARLY DEVELOPMENT
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Fertilization

• union of male and female haploid reproductive
  cells to form a single diploid zygote
• membranes fuse
• male nucleus enters and merges with the female
  nucleus forming zygote

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FERTILIZATION CONTD

• mitosis beginsthe early divisions are called
  cleavage
• during cleavage the cells do not growproducing a
  hollow ball of cells called blastula (the cavity
  is called blastocoel)

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Gastrulation

• an area of blastula collapses creating a
  blastopore (infolded area)
• this process transforms the blastula into a
  multilayered embryo (gastrula)
• the embryo enlarges and develops a deep cavity
  called an archenteron

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Gastrulation--continued

• the layers develop into the following
• Archenteron ------ gut and associated organs
• outer layer -------- ectoderm(skin, hair, nails,
  nervous system..etc)
• inner layer -------- endoderm( surrounds gut)
• most develop a 3rd layer called the mesoderm
  (skeleton, muscles, inner layer of skin,
  circulatory system, lining of body cavity

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PATTERNS OF DEVELOPMENT

• PROTOSTOME
• mollusks, annelids,arthropods
• blastopore develops into mouth
• spiral cleavage
• DEUTEROSTOME
• echinoderms, chordates
• blastopore develops into anus
• radial cleavage

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Coelom formation

• PROTOSTOME SCHIZOCOELY
• cells and the junction of endo/ectoderm rapidly
  divide and form mesoderm
• DEUTEROSTOME ENTEROCOELY
• dorsal (top) part of archenteron divides rapidly
  to develop into mesoderm

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Cleavage types

• PROTOSTOME DETERMINATE CLEAVAGE
• early specialization of the embryonic cells
• DEUTEROSTOME INDETERMINATE CLEAVAGE
• cell specialization occurs later in development
• if it occurs early.can result in identical twins

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Body cavity types

• ACOELOMATES (flatworms)
• no body cavity
• mesoderm is solid
• PSEUDOCOELOMATES (roundworms)
• mesoderm lines the fluid filled coelom
• endodermic gut is suspended in fluid
• COELOMATES
• mesoderm lines body cavity
• surrounds and supports endodermic gut (mollusks,
  annelids, arthropods, chordates, echinoderms)

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