1. You are conducting research on X-chromosome inactivation and have identified
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Question
1.
You are conducting research on X-chromosome inactivation and have identified a strain of mice for which the same X chromosome appears to be always inactivated (ie, the maternal X, based on differences of visible markers on the two X chromosomes). Which of the following could be a possible explanation for your observations?
The Xist promoter is defective on the X chromosome that is inactivated.
The Xist promoter is defective on the X chromosome that is active.
There is no AUG codon present in the Xist gene located on the inactive X.
There is no AUG codon present in the Xist gene located on the active X.
Two of the above are true.
2. You have two strains of E. coli. Strain A has lac operon genotype I+O+P+Z+Y- on its chromosome and lac operon genotype I+O+P+Z-Y+ on an F’ plasmid (F plasmid that contains the lac operon). Strain B has lac operon genotype I+O+P+Z-Y+ on its chromosome and does not have an F plasmid. You do two separate experiments to create a merodiploid (partial diploid) of the lac operon in strain B. Experiment 1 uses conjugation, transferring DNA from strain A to strain B, and experiment 2 uses transduction, also moving lac operon material from strain A to strain B. Which of these two experiments could create a version of strain B that is inducible for lacZ (makes functional B-gal protein only in presence of lactose)?
neither experiment 1 nor experiment 2
both experiment 1 and experiment 2
experiment 1
experiment 2
3. Which region(s) of a eukaryotic gene is/are NOT found within the mature mRNA transcript?
transcription termination region
stop codon
promoter region
a and b
a and c
4. A human microRNA (miRNA) and a human siRNA both have the sequence 5’-CUAGUCAGUCCAAGCAAUUGC-3’. What possible effects might these small RNAs have on an mRNA with the following sequence?
5’-AUCUGAGCAAUUGCUUGGACUCAGUAGGCGCAUUCUAG-3’
The siRNA will prevent translation of the mRNA while the miRNA will have no effect on its stability or translation
The miRNA and siRNA will both lead to cleavage of the mRNA and the miRNA will prevent translation of the mRNA
The miRNA and siRNA will both lead to cleavage of the mRNA
The siRNA will have no effect on the mRNA while the miRNA will prevent its translation
The miRNA will lead to cleavage of the mRNA and the siRNA might either cleave the mRNA or prevent translation of the mRNA
a.The Xist promoter is defective on the X chromosome that is inactivated.
b.The Xist promoter is defective on the X chromosome that is active.
c.There is no AUG codon present in the Xist gene located on the inactive X.
d.There is no AUG codon present in the Xist gene located on the active X.
e.Two of the above are true.
Explanation / Answer
1. Option B. The Xist promoter is active in inactivated chromosome and not in active X chromosome.
2. Option D- Transduction, Since by conjugation only plasmid genome will be transferred in strain A the plasmid gene is mutant for lac Z hence active lac Z is possible by transduction which involved genomic DNA.
3. Option E- Because transcription termination site and promoter region will not be there in mature mRNA.
4. Option C- The mRNA will bind the siRNA and miRNA to form double standard RNA and it will be cleaved.
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