Exam 3 Fall 06 KeyMCB181R Dr. Jorstad

Exam 3 Fall 06 KeyMCB181R Dr. Jorstad - MCB 181R Fall 2006...

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MCB 181R Fall 2006 Instructor: Dr. S. Jorstad Exam III Key (one version only) For multiple choice questions (each worth 3 points), bubble all correct answers (there may be more than one); there is a 1 point penalty for incorrect answer choices. For short essays (each worth 5 points): confine your answers to the space provided on the scansheet; writing outside those margins will adversely affect the machine-scoring of your exam; you may use bulleted points to express yourself, as long as your meaning is clear. Correct answers are bolded; explanations are in red. 1. Which of the following correctly describes the events that take place during the cell cycle? a. During the S phase, DNA is synthesized. * b. During the M phase, there are checking mechanisms to see if the cell is ready to undergo division. (this occurs during G1) c. During G1, the cell grows and synthesizes organelles and cell structures such as endoplasmic reticulum and mitochondria. * d. During G2, the enzyme DNA polymerase would be active. (this is true of S) 2. During which stage(s) of the cell cycle do chromosomes consist of 2 sister chromatids at least part of the time? 3. Cells found in the mucus of smokers often show mutations in the gene that produces the protein p53. Which of the following statements about the role of p53 is/are correct? 4. Differences between mitosis and meiosis include a. Homologous chromosomes do not associate during mitosis. * (they are independent of one another in mitosis) b. Crossing-over occurs during mitosis only. (should be meiosis) c. Mitosis generates haploid cells; meiosis generates diploid cells. (reverse is true) d. The separation of sister chromatids occurs only in mitosis. (it occurs in meiosis II) 1
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e. The purpose of mitosis is to generate genetic diversity; the purpose of meiosis is to make exact copies of cells. (reverse is true) 5. Useful genetic variation is generated in the production of gametes a. When homologous chromosomes separate into different gametes * (contributions of individuals parents are reshuffled) b. During crossing-over between homologous chromosomes.* c. In the separation of sister chromatids at Anaphase of mitosis. (mitosis does not produce gametes) d. During the replication of DNA in the S phase of the cell cycle. (any mutation that occurs here would not be considered “useful genetic variation”) e. In the orientation of the tetrads (homologous pairs) at Metaphase I. * 6. Consider mitotic and meiotic divisions occurring in an organism that has 3 pairs of chromosomes; thus, the diploid number equals six (2n=6). Which of the following
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