MICROANATOMY

Detailed explanation-1: -When a gene is turned off, it no longer provides the directions for making proteins. This means that the proteins needed to fulfill a particular job–say, tolerate lactase–aren’t produced.

Detailed explanation-2: -Only a fraction of the genes in a cell are expressed at any one time. The variety of gene expression profiles characteristic of different cell types arise because these cells have distinct sets of transcription regulators. Some of these regulators work to increase transcription, whereas others prevent or suppress it.