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5.12Summary

  • Our body structure is formed from three germ layers—the endoderm, mesoderm, and endoderm.
  • Various organs are formed through interactions (inducing effects) among the germ layers.
  • The first organ formed is the neural tube, which develops into the brain and spinal cord.
  • Homeotic genes determine what kind of tissue or organ will be formed from each part of the embryo.
  • Homeotic genes are also thought to be involved in changes in the physical structure during the evolution of animals.
  • Animal bodies grow until they reach their breeding period. Their bodily functions also develop. However, once the breeding period has passed, senescence begins, and the animal eventually dies.
  • Senescence is a universal phenomenon in animals, and genetic and environmental factors affect the progression.
  • Germ cells and normal somatic cells have different fates. Germ cells pass on both themselves and their genetic information to the next generation.
  • Embryonic cells during early development have the potential to become various kinds of cells, but then gradually lose this ability as development progresses.
  • However, there are still cells (somatic stem cells) in our body that have the potential to develop into various other kinds of cells.
  • The door is now being opened to a new medical treatment—regenerative medicine—that uses these stem cells.

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