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Pattern Formation and Induction

Pattern Formation and Induction - physical contact or...

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Pattern Formation and Induction | Blastulation and gastrulation establish the main body axis. Organ formation occurs in the next stage of the development of the embryo. During organ formation, cell division is accomplished by migration and aggregation. Pattern formation is the result of cells "sensing" their position in the embryo relative to other cells and to form structures appropriate to that position. Gradients of informational molecules within the embryo have been suggested to provide the positional information to cells. Homeobox genes are pattern genes; they coordinate with gradients of information molecules to establish the body plan and development of organs. Induction is the process in which one cell or tissue type affects the developmental fate of another cell or tissue. As a cell begins to form certain structures, certain genes are turned on, others are turned off. Induction affects patterns of gene expression through
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Unformatted text preview: physical contact or chemical signals. Formation of the vertebrate eye is a well known example. Human Development Fertilization, the fusion of the sperm and egg, usually occurs in the upper third of the oviduct. Thirty minutes after ejaculation, sperm are present in the oviduct, having traveled from the vagina through the uterus and into the oviduct. Sperm traverse this distance by the beating of their flagellum. Of the several hundred million sperm released in the ejaculation, only a few thousand reach the egg. Only one sperm will fertilize the egg. One sperm fuses with receptors on the surface of the secondary oocyte, triggering a series of chemical changes in the outer oocyte membrane that prevent any other sperm from entering the oocyte. The entry of the sperm initiates Meiosis II in the oocyte. Fusion of the egg and sperm nuclei forms the diploid zygote....
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