Use the Following Information When Answering the Corresponding Question(s)

Use the following information when answering the corresponding question(s) .
The lac operon is used in countless ways for genetics research and biotechnology.One important use of the lac operon is to regulate the expression of cloned genes.In this application,some regulatory elements of the operon are fused to the cloned gene that is to be regulated.One application of such technology was reported by Cronin et al. ,The lac operator-repressor system is functional in the mouse,Genes and Development 15 (2001) :1506-17.These investigators fused a portion of the lac operon to the mouse tyrosinase gene,a gene required for pigment production.This recombinant DNA,composed of E.coli lac operon sequences and the mouse tyrosinase gene,was introduced into albino mice using techniques that will be described in Chapter 19.Using the lac operon regulatory sequences,the investigators were able to regulate tyrosinase gene expression.In fact,they were able to convert albino (white) mice into brown mice.The following questions ask you to use your knowledge of the lac operon to deduce how Cronin et al.were able to regulate tyrosinase gene expression in mice.
-Refer to the paragraph about the lac operon experiment by Cronin et al.Introducing the recombinant lac operon/mouse tyrosinase DNA into mice is only half of the equation for regulating tyrosinase.In addition to lac operon/mouse tyrosinase DNA,what other gene must be added to mice to regulate tyrosinase expression?

A) the lacZ gene
B) the lacY gene
C) the lacI gene
D) the lac operator