MCB164S09MTIIpractice+problemskey

MCB164S09MTIIpractice+problemskey - MCB164S09 Practice...

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MCB164S09 Practice problems for MTII 5/11/2009 1. Exposure of S. pombe to conditions of high osmolarity leads to the activation of atf1 + , a stress- induced transcription factor. A number of upstream genes in the signaling pathway, beginning with “Osmostress” and ending with “Atf1 induction” have been identified and have been ordered as follows based on epistasis analysis using both null and dominant gain-of-function alleles. osmostress win1+ wis1+ spc1+ Atf1 induction Atf1 is expressed in a dominant wis1-DD mutant, even in the absence of osmostress. If you were to screen for suppressors of this aberrant Atf1 expression phenotype, what types of alleles (i.e. dom/rec; in which genes/pathways etc.) would you expect to isolate? Recessive loss-of-function mutations in genes downstream of wis1+ involved in Atf1 induction, such as spc1+ ; recessive loss-of-function mutations in the wis1-DD allele; and dominant or recessive mutations in parallel pathways involved in Atf1 induction. Mutations in genes upstream of wis1+ will not be isolated. 2. You have identified a chemical signal (CS) specifying neural development in Drosophila legs. Precursor cells form neurons in the presence of CS, while in the absence of CS these cells differentiate into leg bristles. You have isolated both dominant and recessive mutations in two different genes apparently affecting neuron differentiation. Dominant Neu D mutations and recessive epi- mutations form neurons even in the absence of CS while recessive neu- mutations and dominant Epi D mutations form leg bristles even in the presence of CS. A neu- epi - double mutant forms neurons with or without CS. Based on these data propose a pathway for the regulation of neuron differentiation and specify if the wild type Neu and Epi genes would normally be OFF or ON in the presence or absence of CS. Use arrows to show positive regulation and bars to show negative regulation. Present ON OFF Neurons Absent OFF ON Bristles CS Neu Epi Neuron formation
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3. You have taken the family history of a patient with retinoblastoma (frequent occurrence of tumors of the retina). You determine that the disease appears to segregate as an autosomal dominant trait (see pedigree). You isolate tumor cells and determine the DNA sequence of the Rb gene present in these cells. You only recover the DNA sequence of a common null allele ( Rb - ) but no wild type allele ( Rb + ). From these data and what you know about the inheritance of retinoblastoma answer the following questions. Assume the Rb - phenotype is completely penetrant. A. What is the likely genotype of the tumor cells? Rb-/Rb- B. What are the likely genotypes of the patient’s parents? Father -Rb-/Rb+ Mother Rb+/Rb+ C. Describe two possible mechanisms leading to the genotype of the tumor cells.
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This note was uploaded on 04/04/2010 for the course MCB 164 taught by Professor Burgess during the Spring '08 term at UC Davis.

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MCB164S09MTIIpractice+problemskey - MCB164S09 Practice...

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