You have devised genetic screens to identify gain- and loss-of-function mutations in the Escherichia coli DNA ligase gene. One of the screens (1) seeks mutant cells that are infected more readily with a ligase-deficient strain of T4 phage. The other screen (2) seeks mutant cells that have increased radiation sensitivity at high temperatures. Indicate whether each of the following descriptions better applies to screen 1 (1) or screen 2 (2). Your answer would be a three-digit number composed of digits 1 and 2 only, e.g. 122.
( ) It would identify gain-of-function DNA ligase mutants.
( ) It would identify loss-of-function DNA ligase mutants.
( ) It would identify conditional mutants.

Question

You have devised genetic screens to identify gain- and loss-of-function mutations in the Escherichia coli DNA ligase gene. One of the screens (1) seeks mutant cells that are infected more readily with a ligase-deficient strain of T4 phage. The other screen (2) seeks mutant cells that have increased radiation sensitivity at high temperatures. Indicate whether each of the following descriptions better applies to screen 1 (1) or screen 2 (2). Your answer would be a three-digit number composed of digits 1 and 2 only, e.g. 122.
( )	It would identify gain-of-function DNA ligase mutants.
( )	It would identify loss-of-function DNA ligase mutants.
( )	It would identify conditional mutants.

Quizplus · Accepted Answer

The ligase-deficient phages would readily infect cells that have increased ligase activity. Since ligase activity is required for DNA repair, loss-of-function DNA ligase mutants show radiation sensitivity.

You Have Devised Genetic Screens to Identify Gain- and Loss-Of-Function