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BIOL 121 (2011) Fall Exam 3 + Key

List three possible explanations for these

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Unformatted text preview: choices in matings needed to clearly demonstrate maternal effects and not imprinting or dominance. Several students lost 1 point if the cross(es) used could be also explained by other effects other than maternal effect Several students lost 2 points because they didn’t clearly differentiate between maternal effects and imprinting. For maternal effect, the mom’s genotype will determine children’s phenotype IN WHOLE. . 7 BIOL 121 NAME: Exam 3 12/5/2011 12) a) When E. coli cells are growing on glucose, each cell has approximately 10 molecules of lac repressor protein. When E. coli cells grow on lactose, the number of lac repressor proteins per cell be: (3pts) A) much greater than 10 B) much less than 10 C) approximately equal to 10 Briefly explain your reasoning. (6 pts) Answer: The number of repressor proteins per cell will be approximately equal to 10. The lacI promoter is constitutive. In particular, the level of transcription does not depend on the presence or absence of lactose. Therefore the amount of protein is not affected by growth on glucose versus lactose. GRADER NOTE: a) For the first part (multiple choice), the student either got the answer right or wrong. There was no partial credit. For the second part of the question, 5 points were awarded for explaining that the transcription does not depend on the presence or absence of lactose. Another acceptable answer was that the repressor is not destroyed but rather just inactivated by the presence of lactose. 1 point was awarded for knowing that the lacI promoter is constitutive, if you did not indicate this...
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