animal reproduction

• Stages in animal development

  1. Gametes

  2. Fertilization

  3. Embryonic Development

  4. Post Embryonic Development
• Gametes


  The cells produced by the process of meiosis, which differs from mitosis in that only one of each chromosome ends up in the cells after division
• Male gamete (sperm)


  • Small and almost always flagellated
• Female gamete (egg)


  • Usually large since it contains yolk, and spherical
• Fertilization


  1. A single sperm penetrates and adds its chromosomes to those in the egg

  2. Fertilization cone is produced to push the original sperm into the egg quickly

  3. Fertilization membrane expands around the egg and pushes away other sperm cells
• Embryonic Development


  1. Cleavage Stage

  2. Morula Stage

  3. Blastula or Blastocyst Stage

  4. Gastrula or Primitive Streak
• Cleavage Stage


  The first identifiable period of embryonic development as the fertilized egg begins to divide, with each cell produced called a blastomere
• Morula Stage


  Continued division leads to a solid ball of cells
• Blastula or Blastocyst Stage


  The cells form a hollow sphere, with the cavity inside called the blastocoel
• Gastrula Stage


  A depression forms at one end of the embryo, cells move in to form a saclike pouch, with the cavity of this new pouch called the archenteron which opens to the outside through the blastopore
• Post Embryonic Development


  1. Larvae

  2. Nymphs

  3. Fetus
• Larvae


  • Freeliving forms that resemble the adult, but live and feed independently
  • Each phylum and sometimes each class usually has its own characteristic larvae
  • Similar larvae imply similar ancestry, indicating that the phyla are relatively closely related
• Larval forms


  • Planula
  • Trochophore
  • Nauplius
  • Bipinnaria
• Nymphs


  Immature stages of animals that at least somewhat resemble the adult of the species and that live and feed independently
• Fetus


  An immature stage of vertebrates (higher animals) that does resemble the adult but is usually completely dependent on the mother for nutrition and protection
• Monozygotic twins


  • Developed by the splitting of a fertilized embryo into two
  • Genetic codes are nearly identical
  • Gender is the same
  • Blood types are the same
  • Appearance is extremely similar but may be affected by environmental factors
• Dizygotic twins


  • Developed by two separate simultaneous fertilization events
  • Genetic codes are same as any other sibling
  • Gender is different
  • Blood types are different
  • Appearance is similar as any other siblings