Practice Questions

TLS Online TPP Program

#Question id: 15637

You have isolated two mutations in the Lac operon that cause constitutive expression of Lac genes. You designate these mutants Lac1– and Lac2–. Making use of an F' that carries the Lac operon with the LacY gene mutated, you construct strains that you test for both ß-galactosidase activity and Lac permease activity with results shown below.

Classify each mutation as dominant or recessive and as cis- or trans-acting, giving the experimental result that allows you to arrive at each conclusion. Finally, deduce what type of Lac mutation best fits the properties of Lac 1– and of Lac 2–.

#SCPH28 | Zoology

Lac1- best fits the properties of LacO^c mutations (cis-acting dominant) and Lac2- best fits the genetic characteristics of LacI^-d mutations (trans-acting dominant).
Lac1- best fits the properties of LacI^-d mutations (cis-acting dominant) and Lac2- best fits the genetic characteristics of LacO^c mutations (trans-acting dominant).
Lac1- best fits the properties of LacO^c mutations (trans-acting dominant) and Lac2- best fits the genetic characteristics of LacI^-d mutations (cis-acting dominant).
Lac1- best fits the properties of LacI^-d mutations (cis-acting dominant) and Lac2- best fits the genetic characteristics of LacO^c mutations (trans-acting dominant).