Practice Questions

TLS Online TPP Program

#Question id: 15638

You have isolated two mutations that show decreased expression of the Lac operon. However, unlike like the promoter mutations, these mutations don’t respond to the inducer IPTG. These mutations, designated Lac3– and Lac4–, are evaluated for the quantity of ß-galactosidase and permease activity expressed with or without IPTG:

Mapping experiments reveal that Lac3– and Lac4– are different short deletions located in the region before the start of the LacZ gene. Given the data shown above suggest which genetic element(s) in addition to part of the promoter has been deleted in each mutant.

#Unit 13. Methods in Biology

In Lac3-, a part of LacI is deleted in addition to the promoter and In Lac4-, a part of LacO is deleted in addition to the promoter
In Lac3-, a part of LacO is deleted in addition to the promoter and In Lac4-, a part of LacI is deleted in addition to the promoter
Lac3- best fits the properties of LacO^cmutations (cis-acting dominant) and Lac4- best fits the genetic characteristics of LacI-d mutations (trans-acting dominant).
In Lac3-, a part of LacI is deleted in addition to the promoter and In Lac4-, a part of LacI is also deleted in addition to the promoter.