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2007 exam IV answers

2007 exam IV answers - Name:ANSWERS page 1 Biology 205 exam...

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Name: ANSWERS page 1 Biology 205 exam IV, May 4, 2007 You have two hours. Feel free to draw pictures to help answer the questions. 1) [10 points] The following diagram of C. elegans vulva development shows the fates of several precursor cells. a) What effect would ablating the indicated cells (i.e. killing them with a laser beam) on this development? i) ablate the anchor cell no vulva; all cells become epidermis ii) ablate P4p no effect on vulva (fewer cells contribute to the epidermis) iii) ablate P5p P4p then acquires secondary fate b) In each case in which these ablation experiments reveals the action of a signal, indicate which cells are sending and receiving the signal. i) AC signals to P5p, P6p and P7p ii) AC now signals to P4p also; P6p may signal to adjacent cell (normally P5p but instead P4p if P5p is ablated) 2) [9 points] a) On the following diagram of an Arabidopsis root, indicate i) the quiescent center (QC), ii) the stem cells, and iii) which cells are dividing most often. QC are the cells with darkest shading in diagram Stem cells surround QC Fastest division occurs in cells above the stem cell region b) The WUSCHEL protein (WUS) regulates shoot apical meristem maintenance. Recently a very similar protein called WOX5 was found that appears to have an analogous role in maintaining the root meristem. The WOX5 gene is expressed specifically in the quiescent center. In a wox5 null mutant, what do you suppose happens to the structure of the root? You may use a sketch as part of your answer. Indicate which cells are likely to be changed, and how. Stem cells differentiate instead of dividing.
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Name: ANSWERS page 2 3) [21 points] Flowering of Arabidopsis is induced by long days. a) How do long days and consequent induction of flowering affect each of the following? In each case, indicate which cells are affected.
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