• While the developmental processes of organisms are diverse, a number of common basic mechanisms are found.
  • In the various phenomena that occur during the early stages of development (such as the determination of embryo directionality and the destiny of germ cells), substances derived from the mother (maternal factors) stored in the egg play important roles.
  • As development proceeds, the embryo is roughly compartmentalized into regions. The fates of these regions (i.e., determination of which ones will form the various tissues and organs) are then decided by the expression of homeobox genes.
  • The proteins translated from homeobox genes are transcription factors, which have been well conserved in the evolutionary process. These play an important role in forming the bodies of organisms.
  • Throughout the development process, induction occurs in which cells in certain regions influence those in adjacent regions. There are several induction patterns, but in each case, induction causes the expression of new genes in target cells, thereby determining the fate of those cells.
  • Germ layers are formed in many animals, and interaction among these layers causes the formation of tissues and organs. The large-scale morphogenetic movement that occurs in the early stages of development allows the formation of these germ layers and the subsequent interaction among them.
  • It is now possible to compare the genes involved in the development of nematodes and fruit flies with those involved in human development. As a result, it has been shown that genes with a similar structure play similar functions in each. This indicates that the basic mechanisms forming the bodies of organisms have been continuously passed on during the course of evolution and function in a similar way in the formation of the human body.

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