MCB164+S09+final+practice - 1 MCB164 S09 Practice problems...

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MCB164 S09 Practice problems for the final exam 1. You are interested in mapping the X-chromosome inactivation center in cats and have obtained feline embryonic stem (ES) cell lines from a colleague. You treat the cells with X-rays and find several lines that carry an X chromosome-to-autosome translocation based on Geimsa staining of spread metaphase chromosome preparations. For each cell line you can tell if the autosomal region is inactivated by immunostaining with antibodies specific to MacroH2A.You tabulate the following data where the solid lines represent aligned region of the translocated X chromosome and the dotted lines represent the autosome to which the X-chromosome region is fused (not aligned): A. To which region of the X chromosome does the XIC presumably map? B. What gene would you expect to find expressed at the XIC on the inactive X chromosome C. You are able to create a deletion of the XIC on one chromosome and create a X xic / X XIC+ heterozygote. What pattern of X inactivation do you expect? Circle the answer below: I. random II. X xic is always inactive while X XIC+ is always active III. X xic is always active while X XIC+ is always inactive D. Name three properties of chromatin associated with the inactive X chromosome. B. You have defined a region that you think contains the XIC. What features of Xist RNA might help you to determine if the XIC in cats contains a similar gene? 1 Macro H2A staining A B C D E F X-chromosome - - + + +
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2. The gypsy insulator of Drosophila was first identified within the gypsy tranposable element. The insulator is composed of a 350-bp sequence and is bound by at least two proteins, suppressor of Hairy-wing [su(Hw)] and mod(mdg4). Results from immunofluorescence experiments using antibodies against su(Hw) indicate that this protein is present at hundreds of sites in the genome when spread chromosome preparations are analyzed. These sites do not contain copies of the gypsy element and are presumed to be endogenous insulators, similar to the one found in gypsy . Surprisingly, similar immunofluorescence experiments using intact interphase nuclei of diploid cells do not show such a large number of individual binding sites. Instead, the su(Hw) protein is present in 20 to 25 specific locations within the nucleus. Provide an explanation for this observation. 3. Match the chromatin component most likely associated with the following processes or events. _____ Often found in association with active gene expression _____ Characteristic of imprinted loci in mammals _____ Likely involved in assembly of the kinetochore _____ Consequence of double-stranded RNA expressed from cenH region in S. pombe. A. Histone methylation B. Cytosine methylation C. Histone phosphorylation D. Histone variant E. Histone acetylation 4. Four genes in yeast are required for silencing of a reporter gene positioned near a telomere: RAP1, SIR2, SIR3 , and SIR4 . Rap1 protein binds to a specific DNA sequence found only at telomeres. Binding of Rap1 recruits Sir3 and Sir4, which can also bind to
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MCB164+S09+final+practice - 1 MCB164 S09 Practice problems...

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