Which of the following is not thought to have contributed to the many mass extinction events that have occurred through Earth's history?
A. plate tectonics
B. habitat loss
C. meteorite impacts
D. continental drift
E. punctuated equilibrium
Ans: E. punctuated equilibrium
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A. true B. false
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You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C
You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could not be responsible for the behavior of this strain of yeast? (a) inactivation of a protein kinase that acts on the mitotic Cdk kinase (b) inactivation of an enzyme that ubiquitylates M cyclin (c) inactivation of a phosphatase that acts on the mitotic Cdk kinase (d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin