Question

The initial discovery of IS elements in bacteria revealed the presence of an element upstream (5′) of three genes controlling galactose metabolism. All three genes were affected simultaneously, although there was only one IS insertion. Offer an explanation as to why this might occur.

(A) The IS element may have occupied or interrupted the normal function of a controlling region related to the galactose genes, which are in an operon with one controlling upstream element.
(B) This IS element might connect all three genes so that it looks like they are affected simultaneously even though only one IS insertion was found.
(C) The IS element can transport from one gene to another and it is probable that the IS element had affected the first two galactose genes and then moved to the third one when it was discovered.
(D) It might be that the IS element caused mutations in the other two galactose genes or gene-regulatory regions, so their functions were damaged or lost.

Answer 1

Correct answer: A

Step-by-step explanation:

Insertion sequences (IS) are transposable elements, which only carry transposition activity genes. They interrupt other regions of the genome.

The discovery of this elements in bacteria revealed a controlling element in the 5´ upstream region of the galactose operon.

This is where the IS element transposed and interrupted its function, affecting all three genes downstream simultaneously.