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University of Alberta
Biology (Biological Sciences)
Michael Harrington

Biology 207 - Answers to Practice questions 4 - Mutations Question 1 The A-gene makes a pre-mRNA with one intron. Make a diagram showing how the pre-mRNA is processed normally and what might happen if there is a mutation in the exon/intron boundary. If the exon/intron sequence is absent because of a mutation the Spliceosome may either not remove the intron or it might remove it incorrectly using a nearby sequence as an exon/intron boundary. In any case the resulting mature mRNA will not have an intact ORF. It is unlikely that the truncated proteins made from these mRNAs would be functional. Question 2 Recall that EMS causes GC-->AT bp substitutions. Consult a genetic codon table to answer this question. a) Can EMS cause nonsense mutations? Use a diagram to show why or why not. EMS can cause nonsense mutations. b) Can EMS revert nonsense mutations? Use a diagram to show why or why not. EMS can not revert nonsense mutations. Question 3 The lacI gene in E.coli has mutational hot spots. Hot spots are sites in a gene that are much more mutable than other sites. The following sequence is from the middle of the wildtype lacI gene: 5’-GTCTGGCTGGCTGGC-3’ One mutant allele, FS25, has an extra 4 bp. a) Explain how this mutation occurred. This region contains a CTGG repeat. The most parsimonious explanation fo
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