| quantum models of speciation |
| Models of evolution that hold that speciation sometimes occurs rapidly as well as over long periods, as the classical theory proposed. |
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| Quaternary Period |
| The most recent geologic period of the Cenozoic Era, the Quaternary began 2 million years ago with the growth of northern hemisphere continental glaciers and the ice age. |
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| quaternary structure |
| In some proteins, a fourth structural level created by interactions with other proteins. Aspect of protein structure determined by the number and arrangement of polypeptides in a large protein such as hemoglobin. |
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