From the zygote, pluricellular organisms are formed by serial mitosis. Would this formation be possible if each cell made by mitosis had an identical life in relation to its antecedent cells? How did evolution solve that problem?
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A multicellular organism contains specialized cells that form during the developmental journey from zygote to adult. This is called cell differentiation and results in the variety of cells one can find in a complex organism--for example, a human contains various cell types including-- epithelial, bone, muscle, phagocytes, lymphocytes and neurons-- each looks unique and performs a specific function that helps maintain homeostasis in the organism. Multicellularity allows an organism to exceed the size that a unicellular organism achieve due to the limitations of the surface area to volume ratio. The zygote is capable of differentiating into all cell types. Although mitosis allows the zygote to become a multicellular organism, the process known as differentiation occurs which allows the zygote to change to a complex system of tissues and cell types. Different cells in an organism can have very different appearances, perform different activities although they all share the exact genome. This is known as gene expression--not every gene is "switched on" in every cell of the organism. Only a fraction of the genes in a cell are expressed at any one time and are controlled by transcription regulators.
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