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4 Cards in this Set
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Define epigenesis
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(~upon formation) is a theory of development that states that new structures arise by progressing through a number of different stages.
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What is preformation theory? give an example
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Preformation theory suggests that all structures exist from the very beginning, they just get larger.
One preformation theory, the theory of the Homunculus suggested that a little human embryo was hidden in the head of every sperm. |
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Define mosaic development
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Mosaic development
depends upon specific determinants in the one-celled zygote that are not divided equally between the daughter cells (asymmetric division). Roux (1880's) destroyed one cell of a two-celled embryo (with a hot pin) to result in ~1/2 frog embryo. Regulative development depends upon interactions between 'parts' of the developing embryo can result in causing different tissues to form (even if parts of the original embryo are removed). Driesch destroyed one cell of a sea urchin embryo at the two cell stage and a normal appearing but smaller sea urchin larvae resulted. |
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What is regulatory development?
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Induction is a type of regulatory development.
This is a process where one tissue directs the development of another tissue. A classical experiment: Spemann & Mangold (1924)- graft of the blastopore lip of one newt onto another! Note: The blastopore is the opening formed in early gastrulation through which cell migrate inside. The Spemann Organizer can induce the formation of an ectopic axis (twinned embryo) |
