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problemset1 - Zoo 470 2012 Problem Set#1 Page 1 Name Kelly...

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Zoo 470 – 2012 – Problem Set #1 Page 1 Name: Kelly Engbring Student Number: 9061526837 1. You perform classic embryology experiments to study how cells differentiate in the new species. a. The polar lobe produced in the one-cell zygote of the new species is inherited by only one of the two cells in the 2-cell zygote. You wish to show that, as in other snails such as Ilynassa obsoleta , cleavage of the zygote produces two daughter cells that are no longer totipotent. Describe one experiment you could perform to demonstrate such lack of equivalence of the two cells in the zygote. In your answer, be sure to clearly state the expected outcome. ( 4 points ) During this first cleavage, cell differentiation has occurred so that the two daughter cells are not able to become any cell. During the first cleavage, one daughter cell forms a polar lobe and the other does not. One could perform an experiment determining if the two daughter cells were totipotent by removing the polar lobe from the daughter cell. If the remaining cells divided normally and produced a normal larva, it would be clear that the two daughter cells are still totipotent after the first cleavage. However, this experiment would show that although the remaining cells divide normally, the larva would be incomplete. The polar lobe has become differentiated to include some endodermal and mesodermal determinants, so after the first cleavage the daughter cells are not totipotent. b. The eyes in Ilynassa larvae are formed from micromeres, i.e., from the group of small cells formed at the 8-cell stage. You believe that eyes are formed by the identical cells in the new species. Describe one experiment that would show that your belief is correct.
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