Molecular Genetics
Exam 3 Summer
2009
i. Relax.
ii. Write your name on the back of the last page only.
1. (10 points) You have a mutant strain of E. coli that produces β-galactosidase in large galactosidase in large
quantities whenever lactose is present in the medium, even if glucose is present also. Propose
two mutations that could produce this effect. For each, tell what gene or site is mutant and how
this mutation would produce the observed phenotype.
2. (10 points) In humans, the gene coding for obliviase is transcribed at high levels in response
to the steroid hormone testosterone. An XY human produces normal levels of testosterone, but
produces little or no obliviase. The coding region of his obliviase gene is normal. Propose two
mutations that could be responsible for this phenotype. For each, tell what gene or site in the
DNA is mutant and explain how the change produces the phenotype.
