Differentiation of organs and tissues in a developing organism is associated with:

What does '$4$' represent in the given figure?

Consider the following statements of gene regulation and select the correct statements $:$
$(A)$ Expression of genes is regulated by metabolic,physiological,or environmental conditions.
$(B)$ Galactose can act as an inducer for the lac operon.
$(C)$ The operator region is adjacent to the promoter elements in most operons.
$(D)$ In the lac operon,lactose is transported into the cell through the action of permease.
$(E)$ Regulation of the lac operon by a repressor is referred to as positive regulation.

Which of the following statements is correct regarding the repressor of the $lac$-operon?

Identify the $INCORRECT$ statement from the following with reference to lac operon.

When $Escherichia$ $coli$ cells are cultured in a medium where $Lactose$ is absent,the $i$ gene of $Lac$ $Operon$ continues to produce repressor $mRNA$,because it is: