bottom-up model

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bottom-up model

One of two proposed mechanisms of spontaneous gastrointestinal tract adenomas. In the bottom up model, a stem cell situated in the base of a crypt acquires mutations in the adenomatous polyposis coli (APC) tumour-suppressor gene, impairing the function of the APC protein. The bottom-up theory holds that adenomas, both familial/hereditary and sporadic, arise from a monoclonal proliferation in the gland crypts (monocryptal adenoma), followed by the multistep process of carcinogenesis.
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This theory, which is consistent with the bottom-up theory, holds that invisible, slow-moving particles make up most of the universe and that giant galaxies can't form earlier than a billion or so years after the birth of the universe.
Shandarin, a protege of Zel'dovich now at the University of Kansas, and their colleagues proposed a new version of the bottom-up theory.
Previous versions of the bottom-up theory, he says, hadn't taken into account this linkage, which drives galaxies into the filamentary patterns seen in the sky.
The competing, bottom-up theory could also account for a few massive clusters, Uson says, but a discovery of several more of these blobs could spell trouble for bottom-up supporters.