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The main processes involved in the embryonic development of animals are: tissue patterning (via regional specification and patterned cell differentiation); tissue growth; and tissue morphogenesis. Regional specification refers to the processes that create the spatial patterns in a ball or sheet of initially similar cells.
Fate mapping shows which tissues come from which part of the embryo at a certain stage in development, whereas cell lineage shows the relationships between cells at each division. [12] A cell lineage can be used to generate a fate map, and in cases like C. elegans, successive fate mapping can be used to develop a cell lineage. [13]
In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5]
At a tissue level, ignoring the means of control, morphogenesis arises because of cellular proliferation and motility. [9] Morphogenesis also involves changes in the cellular structure [10] or how cells interact in tissues. These changes can result in tissue elongation, thinning, folding, invasion or separation of one tissue into distinct layers.
[19] [20] [23] Furthermore, if specific cells were isolated in a petri dish from the whole structure, these cells will still form the structure or tissue they were going to form initially. [19] [20] [23] In other words, the signaling to form a specific tissue is within the tissue not coming from a central organ or system.
As a group, the cells within a morphogenetic field in an embryo are constrained: thus, cells in a limb field will become a limb tissue, those in a heart field will become heart tissue. [6] Individual cells within a morphogenetic field in an embryo are flexible: thus, cells in a cardiac field can be redirected via cell-to-cell signaling to ...
Some animals, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Other animals such as bilaterians produce a third layer (the mesoderm) between these two layers, making them triploblastic. Germ layers eventually give rise to all of an animal's tissues and organs through the process of organogenesis.
A concept map typically represents ideas and information as boxes or circles, which it connects with labeled arrows, often in a downward-branching hierarchical structure but also in free-form maps. [ 2 ] [ 3 ] The relationship between concepts can be articulated in linking phrases such as "causes", "requires", "such as" or "contributes to".