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
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:
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